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WORKING    DETAILS    OF 
A    GAS    ENGINE    TEST 


INCLUDING 


A  METHOD  OF  DETERMINING  THE 
TEMPERATURES  OF  EXHAUST  GASES 


BY 
ROBERT  HEYWOOD  FERNALD,  M.E.,  MA. 

Sometime  University  Fellow  in  Applied  Science 
at  Columbia  University 


Submitted  in  partial  fulfilment  of  the  requirements  for 

the  degree  of  Doctor  of  Philosophy,  in  the  Faculty 

of  Applied  Science,  Columbia  University 


NEW  YORK  CITY 

1902 


IJSTTKODUCTIOK 

THE  work  embodied  in  the  following  pages  is  but  a  small  begin- 
ning toward  the  development  of  an  investigation  of  some  impor- 
tance to  the  engineering  and  commercial  world — the  standardiza- 
tion of  methods  of  comparison  of  gas  engines. 

With  the  heterogeneous  collection  of  gas  and  oil  engines  thrown 
upon  the  market  to-day,  some  method  of  standardization  is  very 
essential,  but  the  problem  is  one  of  too  great  magnitude  to  be  com- 
pleted in  the  brief  period  of  one  college  year,  and  it  is  the  hope 
of  the  writer  that  some  one  may  take  up  the  work  where  it  has 
been  dropped. 

The  general  scheme,  as  roughly  outlined,  is 

1.  The  history  and  development  of  the  explosive  engine. 

2.  The  gas  engine  of  to-day,  and  a  comparison  of  existing  en- 
gines, resulting  in  a  classification  into  types  and  a  study  of  these, 
including : 

(a)  A  complete  bibliography  of  the  subject,  together  with  a  list 
of  patents  granted,  both  in  this  country  and  abroad. 

3.  An  investigation  of  the  physical  and  mathematical  problems 
involved,  both  quantitative  and  qualitative. 

4:.  A  complete  and  detailed  method  of  testing  explosive  engines, 
leading  to 

(a)  A  criticism  of  points  of  design  and  construction  and  sug- 
gested improvements,  based  upon  information  obtained  through 
2  and  3. 

5.  General  conclusions  derived  from  the  tests  and  observation, 
coupled  with  a  comparison  of  the  explosive  engine  with  certain 
types  of  non-explosive  engines. 

The  historical  section  has  been  fairly  well  developed  by  previous 
investigators.  It  is  seen  at  once  that  sections  2,  3  and  4  are  to 
a  certain  extent  interdependent  and  that  a  thorough  investigation 
of  one  involves  certain  information  obtained  from  the  others.  A 
brief  inspection  of  the  outline  of  procedure  indicates  that  the  main 
portion  of  section  4  is  at  the  present  time  of  greatest  moment,  and 
the  complete  and  detailed  method  of  testing  explosive  engines  has, 


IV  INTKODUCTION. 

therefore,  received  the  entire  attention  of  the  writer  for  several 
months  past. 

To  avoid  the  possibilities  of  duplicating  work  already  well  under 
way,  or  completed,  a  special  trip  was  made  to  three  technical  insti- 
tutions known  to  be  especially  interested  in  this  subject,  namely : 
the  Massachusetts  Institute  of  Technology,  Boston,  Mass. ;  Wor- 
cester Polytechnic  Institute,  Worcester,  Mass. ;  and  Cornell 
University,  Ithaca,  N.  Y. 

Although  more  or  less  work  upon  the  heat  engine  has  been  car- 
ried on,  or  is  no  win  progress  at  the  laboratories  of  these  institutions, 
yet  the  lines  followed  are  quite  different  from  those  undertaken 
by  the  writer,  and  the  field  for  thorough  research  was  found  prac- 
tically clear,  as  the  greater  part  of  the  work  done  is  of  the  nature 
of  ordinary  commercial  tests  for  the  benefit  of  students  taking 
the  regular  laboratory  courses. 

Correspondence  and  inquiry  led  to  the  belief  that  nowhere  had 
research  been  undertaken  on  the  plan  outlined  above,  and  prep- 
arations were  at  once  made  for  carrying  on  the  investigations. 
The  engines  in  the  laboratory  at  Columbia  University  in  New  York 
City  were  put  into  commission  and  used  for  experimental  pur- 
poses, the  greater  part  of  the  data  being  obtained  from  an  eight 
horse-power  Otto  engine  and  a  five  horse-power  Nash  engine. 

The  results  of  the  investigation  have  been  prepared  for  presen- 
tation before  the  American  Society  of  Mechanical  Engineers  at 
their  meeting  in  Boston,  in  May  1902,  which  accounts  for  the 
form  in  which  they  are  presented. 

The  volumes  of  Transactions  and  numbers  of  papers  to  which 
references  are  made  in  the  text  and  footnotes  are  those  issued  by 
the  American  Society  of  Mechanical  Engineers. 

The  writer  desires  to  express  his  appreciation  of  courtesies  ex- 
tended and  valuable  assistance  rendered,  to  Prof.  F.  E.  Hutton, 
Prof.  R.  S.  Woodward,  Prof.  W.  L.  Cathcart,  Prof.  W.  Hallock, 
Mr.  F.  A,  Goetze,  and  Mr.  C.  E.  Lucke. 

New  York  City,  March  15,  1902. 


PAKT    I. 

WORKING  DETAILS  OF  A  GAS  ENGINE  TEST. 


WORKING    DETAILS 


OF  A 


GAS    ENGINE    TEST. 


1.  .CONSIDERING  the  rapid  advance  of  the  gas  1£  engine   during 
the  past  few  years,  it  is  surprising  to  find  how  little  has  been  done 
toward  standardizing  such  engines,  or  at  least  toward  adopting 
some  form  of  test  whereby  a  definite  idea  of  the  relative  merits 
of  different  engines  can  be  obtained.     Of  late  years  the  market 
has  been  crowded  with  various  types  and  modifications  of  heat 
engines,  especially  of  the  explosive  type,  many  of  which  are  mere 
freaks  and  of  little  or  no  value. 

2.  Although  a  very  few  types  have  received  the  careful  attention 
of  the  expert,  many  engines  thrown  upon  the  market  are  the  re- 
sults of  a  desire  to  invent,  with  the  possible  chance  of  "  hitting 
the  right  thing,"  or  the  product  of  dull  times  in  machine  shops. 

Although  in  the  case  of  the  steam  engine  occasional  forms  are 
produced  having  entirely  new  features,  yet  the  tendency  is  to  con- 
form closely  to  a  general  standard  which. usage  and  careful  inves- 
tigation have  shown  to  be  desirable. 

*  For  further  references  on  this  subject  see  Transactions  as  follows: 
No.  0943,  to  be  presented  at  this  (Boston,  1902)  meeting,  "Final  Report  of  Com- 
mittee Appointed  to  Standardize  a  System  of  Testing  Steam  Engines." 
Vol.  xxii.,  p.  152  :  "Efficiency  of  a  Gas  Engine  as  Modified  by  Point  of  Igni- 
tion."    C.  V.  Kerr. 

Vol.  xxii.,  p.  612;  "Efficiency  Tests  of  a  One-hundred  and  Twenty-five  Horse- 
power Gas  Engine."     C.  H.  Robertson. 

f  The  term  "  gas  engine  "  is  used  throughout  this  paper  to  include  engines 
commonly  termed  oil  engines. 


2  WORKING   DETAILS   OF  A  GAS  ENGINE   TEST. 

3.  Similar  standards  should  be  adopted  for  the  gas  engine  as 
rapidly  as  possible.     This  does  not  prohibit  or  discourage  inven- 
tion or  modification,  which  are  very  essential  in  the  present  con- 
dition of  these  engines,  but  something  should  be  done  to  classify 
and  standardize  those  already  on  the  market,  thus  determining 
what  experience  and  study  have  thus  far  shown  to  be  good  form. 

The  problem  in  its  entirety  is  a  large  one,  and  will  require  many 
months  or  perhaps  years  of  continued  investigation  and  study. 
With  this  fact  in  mind,  the  writer  has  undertaken  a  few  months' 
study  of  the  subject,  and  although  unable  more  than  to  begin  the 
work,  the  results  so  far  obtained  may  prove  of  interest  to  this 
Society. 

4.  Before  the  engines  can  be  standardized  some  definite  method 
of  determining  the  relative  merits  of  different  engines  must  be 
settled  upon,  and  this  leads  at  once  to  the  necessity  of  a  standard 
method  of  testing  gas  engines,  which  will  form  the  special  part  of 
the  problem  herein  discussed. 

It  is  of  interest,  before  taking  up  in  detail  the  method  of  con- 
ducting the  tests,  to  note  some  of  the  items  that  require  careful 
investigation  and  study  for  a  proper  classification  of  the  engines. 
Much  of  the  data  desired  is  simply  for  general  information, 
and  to  obtain  the  views  of  the  manufacturer  on  certain  points  and 
to  determine  what  he  considers  good  practice. 

Other  information  is  needed  because  it  enters  into  any  test  of 
the  engine  that  may  be  made,  while  other  questions  lead  toward 
a  classification  of  such  engines  into  general  divisions.  Although 
time  has  not  permitted  the  testing  of  such  data  sheets  practically, 
yet  the  following  general  form  serves  as  a  basis  for  beginning  the 
investigation  and  experience  alone  can  determine  the  necessary 
modifications  and  additions: 

GAS   ENGINE   DATA. 

No Test  No 

Date 

1.  Name  of  Engine 

2.  Manufactured  by 

3.  Is  it  two  or  four  cycle  ? 

4.  Kind  of  fuel  used 

5.  Assumed  heat  of  combustion  of  fuel  — B.  T.  U.  per 

6.  Actual  horse-power 

7.  Floor  space  occupied 

8.  Height,  wheels  to  clear  floor 

9.  Weight    

10.  Number  of  cylinders 

11.  How  are  cylinders  arranged  if  more  than  one? 

12.  Diameter  and  weight  of  flywheel.     Diam.  = ins.     Wgt.  — Ibs. 


WORKING  DETAILS  OF  A  GAS  ENGINE  TEST. 

13.  Diameter  and  width  of  brake  pulley.     Diam.  = ins.     Width  = ins. 

14.  Diameter  of  piston  = ins.     Length  of  barrel  = ins.     No.  rings 

15.  Piston  displacement^ cu.  ft.     Clearance^ cu.  ft. 

16.  Length  of  stroke^ ins.     Length  of  connecting-rod  = ins. 

17.  Revolutions  per  minute=: 

18.  Kind  of  governor 

19.  Method  of  governing 

20.  Special  governor  features     

21.  Kind  of  ignition  :  (A),  hot  tube  ;  (B),  flame  ;  (<7),  electric. 

Tf  ( A  \   J  (a)  location (b)  dimensions 

(c)  how  heated 


Tf  ( T*\   J  (a)  kind (b)  size  of  flame  port . 

>  («)   special  features 


If  (C)  -j 


|  (  (1)  current  required  .........  (2)  voltage.  .  . 

(a)  contact  spark  <  (3)  battery  recommended  ...(4)  number... 
(5)  specifications  of  coil  .....  ............. 

(1)  current  required  ........   (2)  voltage.  .  . 

inrrm  snark  ^  kind  of  plu£  ............  (4)  location  •  • 

J  j.  (5)  battery  recommended.  .  .  .(6)  number  .  . 

(_  (7)  specifications  of  coil  .................. 

22.  Kind  of  valves   ........................................................ 

23.  Special  features  of  valve  mechanism  ..................................... 

24    Diameter  of  (a)  gas  valve  ......  ins.  ;  (6)  air  valve  ......  ins.  ;  (c)  mixture  valve 

......  ins.  ;  (d)  exhaust  valve  ......  ins. 

25.  Lift  of  (a)  gas  valve  ........  ins.  ;  (6)  air  valve  ........  ins.  ;  (c)  mixture  valve 

......  ins.;  (d)  exhaust  valve  ......  ins. 

i(a)  carburettor  ................................................ 
(6)  vaporizer  ................................................. 
(c)  mixer  .................................................... 

27.  Means  of  maintaining  constant  proportions  ............................... 

28.  Method  of  fuel  'feed  .'.'.'.  Y.'.Y.Y.Y.Y.  .  .  .  .  !!.'.'.'!.'.'.'.'."."!!.".'.!.'"!'.'.'!!!!!"!! 

29.  Number  of  water  inlets  ...........  ........  diameters  ..................  ins. 

30.  Number  of  water  discharges  ...............  diameters  ..............    .  .  .ins. 

31.  Best  rate  of  water  feed    ................................................ 

32.  Kind  of  muffler  ........................................................ 

33.  Dimensions  of  muffler  ................................................. 

34.  Does  muffler  use  water?  ........................    ........................ 

35.  Means  for  preventing  noise  at  air  inlet  ................................... 

36.  Kind  of  gas  bag  ........................................................ 

37.  Dimensions  of  gas  bag  ................................................. 

38.  Means  of  clearing  engine  of  exhaust  gases  ......................    ......... 


Devices  for  starting  or  aiding  starting. 


5.  The  investigations  which  have  developed  the  details  of  con- 
ducting tests  have  been  carried  on  at  the  mechanical  laboratory 
of  Columbia  University  during  the  present  college  year.  The 
various  experiments  have  been  developed  largely  from  work  on  a 
6  x  12^  Otto  engine,  and  a  6  x  9  Nash  engine.  Much  time  has 
been  devoted  to  working  out  many  details  and  to  following  inci- 
dental suggestions  that  offered  themselves  as  the  work  progressed, 
and  it  is  proposed  to  present  rather  fully  many  important  points. 

This  may  seem  unnecessary  to  those  already  familiar  with  such 
work,  but  it  is  believed  that  this  part  of  the  paper  may  prove  of 


WORKING  DETAILS  OF  A  GAS  ENGINE  TEST. 


interest  and  value  to  those  who  propose  undertaking  such  tests  for 
the  first  time.  For  this  reason  some  of  the  difficulties  and 
errors  that  are  likely  to  occur  are  especially  emphasized. 

6.  It  is  hardly  necessary  to  offer  any  explanation  of  the  items 
called  for  in  the  "  log  "  of  the  test,  as  information  may  be  ob- 
tained regarding  each  of  these  points  from  the  details  of  the 
corresponding  items  that  appear  in  the  final  report.  The  form 
of  "  log "  appended  is  found  to  be  convenient  for  making  the 
preliminary  records : 

Date 

Log  of Gas  engine  test Test  No 

By 

Object 

Length  of  brake  lever ft. 

Weight  of  brake  lever Ibs. 

Cubic  feet  of  vapor  per  pound  of 

Weight  of  gallon  of Ibs. 

1.  Number  of  run 

2.  Time 

3.  Speed  and  explosions,  revolutions  per  minute,  hand  indicator 

4.  "  "  reading  of  speed  counter 

5.  "  "  explosions  per  minute,  special  count 

6.  "  "  reading  of  explosion  counter 

7.  Total  load  on  scales Ibs. 

8.  Temperatures,  degrees  Fahr.  QJ-  Cent.,  gas 

9.  air  

10.  jacket  water,  entering 

11.  "          "       leaving 

12.  "          "       barrel 

13.  exhaust,  observed 

14.  "        at  pressure  of  atmosphere. .. 

15.  Valve  index  reading,  gas 

16.  "          "          "         air 

17.  Areas  of  valve  openings,  gas  or  vapor , , sq.  ins. 

18.  "  "  "  oil " 

19.  "  "  "  air " 

20.  "  "  mixture , 

21.  "  "  "  exhaust   

22.  Weights  and  volumes,  weight  of  jacket  water Ibs. 

23.  "          reading  of  gas  meter,  cu.  ft or  gals,  of 

24.  "  "         reading  of  air  meter 

25.  "  "          gas  for  igniter cu.  ft. 

26.  Indicator  springs  used,  power  card 

27.  "  "          "      compression  card 

28.  Pressures,,  gas,  inches  of 

29.  air,  inches  of 

80.  jacket  water,  Ibs.  per  sq.  in 

31.          "  exhaust,  Ibs.  per  sq.  in 

Remarks 

7.  Before  entering  upon  a  discussion  of  a  complete  test  of  a 
gas  engine  it  is  necessary  to  establish  certain  standard  units. 
Without  question  the  proper  unit  for  the  energy  derived  from  the 
fuel  used  is  the  "  British  Thermal  Unit,"  which  has  been  adopted 
throughout  this  country  and  England,  and  is  designated  in  this 


WORKING  DETAILS   OF  A   GAS   ENGINE   TEST.  5 

paper  by  the  usual  symbols,  B.  T.  U.  In  like  manner  the  term 
horse-power  is  used  to  designate  the  rate  of  work,  and  I.  H.  P. 
and  B.  H.  P.  have  their  usual  significance,  meaning  indicated 
horse-power  and  brake  horse-power  respectively. 

Further  explanation  of  the  units  used  will  develop  during  the 
examination  of  the  final  report.  It  is  hardly  necessary  to  touch 
upon  the  proper  methods  of  calibration  of  instruments  to  be  used, 
with  the  exception  of  special  instruments  or  instruments  used 
under  special  conditions,  as  this  subject  has  been  so  fully  treated 
in  many  previous  publications.  These  cases  will  be  treated  under 
their  respective  heads. 

PRELIMINARIES    OF    THE    TEST. 

8.  Before  beginning  the  test  it  is  very  essential  to  see  that  the 
engine  is  in  good  running  order,  thoroughly  oiled,  and  properly 
adjusted.     All  valves  should  be  carefully  examined  and  adjusted. 
All  connections  to  the  engine,  whether  fuel,  air,  or  water,  should 
be  tested  for  leakage. 

Special  note  should  be  made  of  any  points  out  of  the  ordinary, 
and  if  they  are  of  such  a  nature  as  to  affect  the  results  of  the  test, 
the  difficulties  should  be  set  right  as  far  as  possible,  and,  when 
this  cannot  be  done,  careful  estimates  should  be  made  of  the 
changes  in  the  results  due  to  such  conditions. 

It  is  of  the  greatest  importance  that  each  observer  know  exactly 
what  is  expected  of  him,  and  that  he  at  least  be  made  thoroughly 
familiar  with  the  details  of  all  apparatus  and  machinery  bearing 
upon  his  portion  of  the  work  and  he  should  be  shown  exactly  what 
to  do  in  case  of  emergency,  in  order  to  rectify  difficulties  as 
quickly  as  possible  without  interrupting  or  possibly  destroying  an 
entire  test. 

9.  In  the  series  of  tests  from  which  the  results  for  this  paper 
were  obtained,  more  than  one  test  was  entirely  lost  after  hours 
of  work  through  the  hasty  action  or  lack  of  judgment  of  some  one 
observer.     Where  possible,  a  picked  and  trained  crew  should  be 
retained,  and  even  then  as  far  as  practicable  the  director  of  the 
test  should  attempt  nothing  but  the  oversight  of  the  observers, 
and  should  stand  ready  for  all  emergencies,  allowing  the  individual 
observer  to  touch  nothing  but  the  instrument  he  is  observing,  and 
then  only  as  directed.     Unfortunate  experience  has  shown  this  to 
be  the  only  possible  way  of  obtaining  reliability  in  results. 

It  is  necessary  that  the  engine  be  run  a  sufficient  time  before 


b  WORKING  DETAILS   OF  A   GAS  ENGINE  TEST. 

the  real  start  of  the  test,  to  enable  all  parts  to  become  properly 
adjusted  to  the  desired  running  conditions,  or  to  get  the  engine 
"  warmed  up/7  and  to  determine  accurately  the  proper  working 
of  all  instruments  and  recording  devices,  and  especially  if  the 
engine  is  to  carry  the  maximum  load  which  it  can  carry  continu- 
ally. Much  difficulty  is  often  experienced  in  determining  this 
maximum  load,  especially  if  the  fuel  used  is  city  gas,  for  then 
the  load  carried  yesterday  may  be  far  from  the  possible  load  of 
to-day.  If  a  brake  is  used  without  cooling  water,  then  the  run 
previous  to  the  start  of  the  test  must  be  of  sufficient  length  thor- 
oughly to  warm  the  brake  pulley,  to  permit  further  expansion  and 
a  sudden  increase  in  the  load.  A  brief  preliminary  trial  should 
in  every  case  precede  the  regular  run,  to  make  certain  that  every 
observer  understands  his  work,  and  it  is  found  advantageous  not 
to  inform  the  observer  of  any  distinction  between  the  preliminary 
run  and  the  true  test. 

The  reading  of  an  ordinary  meter  used  for  measuring  air  supply 
is  not  a  difficult  matter,  but  it  has  been  found  that  few  men  can 
obtain  reliable  readings  without  previous  experience. 

OBJECT    OF    THE    TEST. 

10.  It  is  absolutely  necessary  that  the  object  of  the  test  be  def- 
initely determined,  and  this  object  should  be  kept  constantly  in 
mind  during  the  run,  whether  the  test  be  a  general  efficiency  test, 
a  test  for  proportions  of  air  to  gas,  changes  in  conditions  of  igni- 
tion, temperature  of  jacket  water,  throttling  of  exhaust,  or  what 
not. 

FORM    OF    REPORT    BLANK. 

11.  Careful  study  coupled  with  experience  has  developed  the 
accompanying  form  for  the  final  report  of  the  test.     At  first  sight 
it  may  appear  to  some  as  too  comprehensive,  consequently  cumber- 
some, but  the  desire  has  been  to  secure  a  form  that  will  serve  for 
all  purposes,  whether  for  an  efficiency  test  only  or  for  a  complete 
laboratory  test  in  which  much  data  is  desired  for  further  study 
that  might  of  itself  be  of  little  value  to  the  manufacturer  directly, 
but  of  great  value  scientifically,  especially  along  lines  which  will 
aid  in  further  development  of  the  heat-engine  problem. 

It  is  deemed  wise  to  take  up  each  item  of  the  report  in  detail, 
and,  to  assist  in  making  the  explanations  clear,  run  number  6  has 
been  selected  from  each  of  the  two  tests  chosen,  for  this  paper. 


WORKING  DETAILS   OF  A  GAS   ENGINE  TEST.  7 

The  engine  from  which  the  results  recorded  as  test  "  A  "  were 
obtained  was  run  under  full  load,  while  in  nlaking  test  "  B  "  the 
engine  carried  only  half  load. 

12.  It  is  not  intended  to  draw  any  comparisons  between  the  two 
runs,  and  they  are  both  submitted  simply  to  assist  in  further 
explanations  of  the  method  of  working  out  a  complete  test  if  con- 
ducted on  the  plan  outlined. 


WORKING   DETAILS   OP  A   GAS  ENGINE  TEST. 


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WORKING  DETAILS  OF  A  GAS   ENGINE  TEST.  11 

The  titles  following  paragraphs  are  numbered  to  correspond  to 
the  items  as  they  appear  in  the  report. 

Especial  attention  has  been  given  to  the  arrangement  of  this 
report,  the  items  appearing  in  the  order  in  which  they  are  most 
readily  deduced;  i.e.,  with  one  or  two  possible  minor  exceptions, 
no  solution  is  called  for  for  which  the  data  have  not  already  been 
supplied  by  the  "  log  "  or  by  a  previous  solution. 

1.  Number.     2.  Time  Intervals. 

13.  It  is  necessary  to  make  frequent  readings  during  the  test, 
and  item  1  corresponds  to  the  numbers  of  these  readings.     What 
the  interval  between  readings  shall  be  is  not  material  so  long  as 
the  period  is  sufficiently  long  to  eliminate  errors  that  might  creep 
in  from  too  brief  intervals.      Ten-minute  intervals   are  recom- 
mended in  case  the  total  run  is  not  over  two  or  three  hours.    When 
the  nature  of  the  test  is  such  that  several  hours  are  necessary  for 
the  determination  of  average  results,  or  quantities  of  fuel  used, 
the  time  intervals  may  be  lengthened  as  desired,  although  thirty 
minutes  should  probably  be  the  maximum  time  between  readings. 
When  more  convenient  the  time  interval  will  be  designated  by 
"  int." 

REVOLUTIONS    AND    EXPLOSIONS. 

3.   Total  Revolutions. 

14.  Whenever  possible  a  continuous  speed  counter  should  be 
used,  and  it  is  advantageous  to  obtain  simultaneous  records  from 
two  such  counters. 

It  is  best  to  check  the  readings  during  each  interval  by  a  hand 
indicator,  in  order  that  some  record  may  be  had  in  case  of  acci- 
dent to  the  continuous  recorders — especially  if  one  recorder  only 
be  used. 

The  fluctuations  in  speed  of  a  gas  engine  of  the  single  cylinder 
type  are  so  great  and  so  varied  that  the  readings  of  a  hand  speed 
counter  taken  for  one  minute  are  apt  to  be  far  from  reliable,  and 
dependence  should  be  put  upon  them  only  in  case  of  absolute 
necessity. 

4.  Revolutions  per  Minute  (Mean). 

15.  The  mean  number  of  revolutions  per  minute  is  simply  the 
total  number  of  revolutions  for  the  time  interval  divided  by  the 
number  of  minutes  in  that  interval.     The  mean  speed  thus  ob- 


12  WORKING  DETAILS  OF  A  GAS  ENGINE  TEST. 

tained  is  far  more  reliable  than  that  obtained  by  the  hand  speed 
counter. 

5.  Total  Explosions. 

16.  The  general  remarks  regarding  3  apply.     A  continuous 
counter  should  be  used  whenever  possible  for  determining  the 
number  of  explosions.     This  can  usually  be  done  by  connections 
to  some  stem  or  arm  of  the  inlet  valve,  so  that  the  counter  is 
operated  by  the  movements  of  this  valve.     Care  should  be  taken 
to  see  that  the  ignitions  are  reliable  and  that  every  ignition  gives 
an  explosion. 

Any  method  of  simply  counting  the  misses  by  sound  or  feeling, 
when  they  are  frequent,  is  found  to  be  absolutely  unreliable. 

6.  Explosions  per  Minute  (Mean}. 

17.  These  figures  are  obtained  by  dividing  the  total  number  of 
explosions  for  the  time  interval  (item  5)  by  the  number  of  minutes 
in  that  interval  (item  2). 

7.  Ratio  of  Revolutions  to  Explosions. 

18.  This  item  gives  a  clear  idea  of  the  regularity  of  the  ex- 
plosions.    In  the  single  cylinder  four-cycle  engine  making  no 
misses,  this  ratio  of  the  number  of  revolutions  to  the  number  of 
explosions  would  be  2.00.     Any  decrease  in  the. number  of  explo- 
sions per  minute  would  cause  this  ratio  to  increase,  and  a  hasty 
glance  at  this  item  indicates  at  once  the  regularity  of  the  explo- 
sions.    In  a  single  cylinder  two-cycle  engine  the  corresponding 
ratio  is  1,00, 


WORKING  DETAILS  OF  A  GAS  ENGINE  TEST. 


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16  WORKING  DETAILS  OF  A  GAS  ENGINE  TEST. 

JACKET    WATER. 

8.    Weight  in  Pounds.     9.    Weight  in  Pounds  per  Hour. 

19.  The  simplest  method  of  weighing  the  jacket  water  is  by 
means  of  two  oil  barrels,  with  proper  outlet  pipes,  set  upon  plat- 
form scales.     The  piping  from  the  engine  should  be  so  constructed 
that  the  water  may  be  fed  into  either  barrel  at  will.     It  is  hardly 
necessary  to  take  the  weight  of  the  jacket  water  for  each  of  the 
time  intervals,  provided  the  water  flow  has  been  carefully  regu- 
lated before  the  test  actually  starts  and  the  temperature  of  the 
feed  water  is  found  to  be  constant. 

If  the  flow  is  maintained  so  nearly  uniform  that  the  fluctuations 
in  temperature  of  the  outlet  water  are  not  large — say  for  ex- 
treme range  not  over  15  degrees  Fahr. — the  total  weight  of  water 
for  the  entire  test  may  be  recorded,  and  this  result  divided  into 
equal  proportions  for  the  different  runs. 

20.  Should  the  feed-water  temperature  show  marked  variations, 
which  is  likely  to  be  the  case  if  the  water  from  the  main  passes 
through  several  buildings  before  reaching  the  engine,  it  should 
be  weighed  in  small  amounts  and  the  weight  and  temperature 
entered  on  the  "  log." 

The  weight  per  hour  is  calculated  directly  from  the  values  in 
item  8.  In  case  of  long  runs  it  is  well  to  determine  the  weight 
for  each  hour  and  to  assign  to  each  time  interval  its  proportionate 
part. 

10.  Temperature  Range. 

21.  Keferring  to  items  10,  11,  12  of  the  "  log,"  it  is  noticed 
that  they  are  marked  temperature  of  water  entering,  leaving,  and 
barrel  respectively.     If  the  water  used  comes  through  a  system 
of  pipes  running  through  warmed  buildings,  it  is  best,  if  possible, 
to  allow  the  water  to  flow  long  enough  to  show  fairly  constant 
temperature  before  starting  the  test.     This  is  especially  necessary 
in  winter  when  the  water  is  taken  from  the  city  main — a  difference 
of  45  degrees  Fahr.  is  often  observed  under  these  conditions. 

22.  In  cases  where  the  weighing  barrels  are  near  the  engine 
the  temperature  of  the  discharged  water  may  be  taken  as  it  enters 
the  barrel,  which  is  often  more  convenient  than  to  obtain  the  tem- 
perature just  as  the  water  leaves  the  engine.     It  has  been  found 
advantageous  to  keep  a  record  of  both  when  the  conditions  admit. 
In  the  tests  shown  no  special  attention  was  paid  to  the  best  tern- 


WORKING   DETAILS   OF   A   GAS   ENGINE   TEST. 


17 


perature  of  the  leaving  jacket  water.  In  general  it  seems  to  be 
the  opinion  that  the  hotter  the  water  is  allowed  to  get  without 
injuring  lubrication  or  giving  premature  ignition  the  better. 
Some  authorities  give  160  degrees  Fahr.  as  the  best  temperature 
for  the  discharge.  Experiments  seem  to  indicate  that  pressure 
in  the  water  jacket  is  of  little  moment. 

The  range  of  temperature  is  the  difference  between  the  tem- 
perature of  the  leaving  water  and  that  of  the  entering. 

11.  Maximum  Velocity,  Feet  per  Second. 

23.  This  has  no  direct  bearing  upon  the  test  proper,  but  is  in- 
serted for  use  in  making  comparative  tests  of  different  engines, 
and  for  the  determination  of  points  of  design  of  water  inlets  and 
outlets  for  the  most  effective  results.     The  data  collected  would 
undoubtedly  show  variations  depending  upon  the  method  of  deliv- 
ery, whether  from  natural  circulation  or  forced.     . 

12.  Heat  Absorbed,  E.  T.  U. 

24.  The  heat  absorbed  by  the  jacket  water  is  a  very  large  per- 
centage of  the  entire  heat  supplied — often  about  50  per  cent. 
Since  the  specific  heat  of  water  is  taken  as  unity,  the  calculation 
consists  only  in  multiplying  the  number  of  pounds  of  water  used 
during  the  interval  by  the  range  of  temperature,  this  range  of  tem- 
perature being  equal  to  the  number  of  heat  units  absorbed  per 
pound  of  water. 


Data  Given. 

s  =  specific  beat  of  water  —  1. 
tr'=  temperature  range. 
W=  weight  water  for  time  interval. 

To  Find— 
hw  =  B.  T.  U.  for  the  time  interval. 

Examples. 
"A"  Run  No.  6: 

s  =  \. 

tr  =  72  degrees. 
W  =  97  pounds. 

"B"  Run  No.  6: 

8    =1. 

tr  =  39  degrees. 
W  =  93. 3  pounds. 
2 


Solution. 


hw  =  s  x  tr  x   W. 


hw  =  1  x  72  x  97  =  6,984  B.  T.  U. 


Jiw  -  1  x  39  x  93.3  =  3,640  B.  T.  U. 


18  WORKING   DETAILS   OF  A  GAS   ENGINE   TEST. 


AIR. 


25.  It  is  very  essential  that  the  quantity  of  air  used  be  accu- 
rately measured,  and  the  simplest,  and  usually  most  accessible, 
method  is  by  means  of  a  gas  meter  of  sufficient  size.     The  accu- 
racy of  this  meter  should  be  carefully  determined.     (For.  methods 
of  calibration,  sec  "  Report  of  the  Committee  Appointed  to  Stan- 
dardize a  System  of  Testing  Steam  Engines/7  paper  No.  0943. 

26.  Even  if  the  meter  is  carefully  calibrated  when  working 
under  suction,  the  readings  will  not  be  the  same  when  the  air 
enters  under  pressure,  or  vice  versa.     With  the  setting  of  the 
air  valve  as  used  in  making  test  "  B,"  the  meter  readings  averaged 
for  a  given  number  of  admissions  109.5  cubic  feet  when  working 
under  a  pressure  indicated  by  2  inches  of  water,  and  97.25  cubic 
feet  when  working  under  suction.     The  flow  recorded  by  the 
meter  was  then  1.13  times  as  much  when  working  under  light 
pressure  as  when  working  under  suction. 

The  meter  through  which  the  gas  is  measured  works  at  all  times 
under  slight  pressure,  and  for  accurate  determination  of  the  pro- 
portions of  air  to  gas  the  meter  used  for  air  measurement  for  the 
experiments  upon  which  this  paper  is  based  was  put  under  equal 
conditions  by  supplying  air  under  pressure  by  means  of  an 
Ingersoll  air  compressor.  In  the  absence  of  a  compressor  a 
blower  may  easily  be  arranged  to  accomplish  the  same  result. 
The  method  of  piping  used  is  best  explained  by  reference  to  the 
cut,  Fig.  1. 

27.  A  is  the  main  compressed  air  line  leading  from  the  com- 
pressor to  the  air  meter  B.     C  is  a  relief  tank  filled  with  water 
to  a  depth  corresponding  to  the  head  shown  by  the  manometer 
attached  to  the  gas  pipe,  and  causing  the  flow  of  air  through  the 
meter  to  remain  fairly  constant.     From  B  the  air  passes  through 
the  pipe  D,  directly  to  the  engine  save  for  the  interposition  of  air 
bags  E  and  F  and  an  old  mufiler,  used  for  the  same  purpose  as 
the  bags — namely,  to  reduce  the  variation  in  pressure  of  the  air. 
At  H  is  shown  a  manometer  for  determining  the  air  pressure,  and 
by  means  of  the  inlet  valve  /  this  pressure  can  be  maintained 
the  same  as  that  shown  by  the  gas  manometer.     By  this  method 
an  accuracy  in  determining  the  proportions  of  air  to  gas  was  as- 
sured that  otherwise  could  not  be  guaranteed. 


WORKING   DETAILS   OF   A   GAS   ENGINE   TEST. 


19 


WORKING   DETAILS   OF   A   GAS   ENGINE   TEST. 


13.  Cubic  Feet.     14.   Cubic  Feet  per  Hour. 

28.  In  reading  the  ordinary  meter  it  is  not  sufficiently  accurate 
to  catch  the  readings  by  noting  the  positions  of  the  index  hands 
at  the  beginning  and  close  of  the  time  interval,  but  it  is  necessary 
to  keep  an  observer  at  the  meter  and  require  the  readings  to  be 
taken  from  the  hand  which  indicates  the  single  cubic  feet,  and 
whose  complete  revolution  records  10  cubic  feet. 

The  cubic  feet  per  hour  are  readily  calculated  from  the  data 
for  the  given  time  interval. 

15.  Temperature,  Fahr. 

29.  Under  ordinary  conditions  it  is  sufficient  to  take  the  tem- 
perature of  the  air  at  the  beginning  and  at  the  close  of  the  test, 
but  if  the  conditions  are  variable  more  frequent  readings  will  be 
necessary,          .^», 

16.    Weight  per  Cubic  Foot. 

30.  This  weight  is  that  of  a  cubic  foot  of  air  at  the  temperature 
given  in  item  15,  and  is  found  as  follows: 


Data  Given. 
Wo  —  weight  cubic  foot  air  at   32  de- 

grees Fahr.  =  .0807  pound. 
T0  =  32°  +  459°  =  491°  (absolute). 
Ti  —  absolute  temperature  of  air. 
=  item  15  +  459°. 

To  Find— 
w\  =  vvgt.  per  cu.  ft.  at  given  temp. 

Examples. 
"A  "  Run  No.  6  : 


T,  =  86°  +  459°  =  545 


Run  No.  6:  m 


=  87°  +  459°  =  546°. 


Solution. 


491 
0807  =j~  =  .0727  pound. 


0807  ^  =  .0725  pound. 


17.  Maximum   Velocity  in  Feet  per  Second. 

31.  Like  item  11,  this  has  no  direct  bearing  upon  the  single 
test,  but  is  for  use  in  making  comparative  tests  of  different  en- 
gines and  for  determination  of  points  of  design  of  air-inlet  valves 
for  the  most  effective  results. 


WOBKING  DETAILS   OF  A  GAS  ENGINE  TEST.  21 

18.  Specific  Heat,  Cv. 

32.  The  specific  heat  of  air  at  both  constant  pressure  and  con- 
stant volume  may  be  found  in  any  books  on  thermodynamics. 
The  specific  heat  at  constant  volume,  denoted  by  CVJ  is  the  only 
value  needed  in  this  work — Cm  —  .1691. 


FUEL. 

33.  The  question  of  quantity  of  fuel  used  is  the  first  to  present 
itself,  and  the  methods  of  determining  this  will  depend  entirely 
upon    the    kind    of    fuel.     If    coal    is    required    the    method    of 
determining  the  amount  is  that  usual  in  case  of  boiler  tests,  and 
is  fully  described  in  the  Transactions  of  this  Society,  Vol.  XXL, 
p.   34.     The  method  used  for  ascertaining  the   amount  of  gas 
is  by  means  of  the  standard  gas  meter.     Methods  of  calibrating 
these  meters  are  given  in  the  "Report  of  the  Committee  appointed 
to  Standardize  a  System  of  Testing  Steam  Engines,"  paper  "No. 
.0943.     If  oil  is  used  it  can  easily  be  measured  by  means  of  cali- 
brated tanks.     For  small  engines  using  little  oil,  the  tanks  should 
be  small  in  diameter,  that  the  errors  in  measurement  may  be  re- 
duced as  much  as  possible. 

19.    Cubic  Feet  or  Gallons.     20.   Cubic  Feet  or  Gallons  per  Hour. 

34.  The  method  of  measuring  the  fuel  has  already  been  ex- 
plained.     The    quantities    designated   in   item    19    refer    to    the 
amounts  used  for  the  given  time  interval,  and  if  the  fuel  be  gas, 
this  would  be  the  number  of  cubic  feet  as  read  directly  from  the 
meter. 

If  the  fuel  be  oil  the  number  of  gallons  for  the  period  should 
be  recorded. 

21.  Temperature,  Fahr. 

35.  As  in  the  case  of  air,  it  is  usually  sufficient  to  take  the 
temperature  of  the  gas  at  the  beginning  and  at  the  close  of  the  test, 
but  if  the  conditions  be  variable  more  frequent  readings  will  be 
necessary. 

In  case  of  engines  that  vaporize  oil  fuel  before  it  enters  the 
cylinder,  this  determination  of  temperatures  is  very  difficult,  if, 
indeed,  possible.  There  are  many  forms  of  carburetors,  and  the 
temperatures  of  vaporization  are  found  to  vary  greatly. 


22  WORKING   DETAILS   OF   A   GAS   ENGINE   TEST. 

Further  developments  may  determine  the  desired  method  of 
making  reliable  observations  of  the  temperature  of  this  type  of 
fuel. 

22.    Weight  per  Cubic  Foot  or  Gallon. 

36.  In  case  the  fuel  be  gas,  it  is  not  always  convenient  to  obtain 
the  weight  per  cubic  foot.     If  the  temperatures  of  the  air  and 
gas  be  the  same,  this  is  hardly  necessary,  and  even  when  these 
temperatures  be  different  the  necessity  of  knowing  this  weight  is 
not  sufficient  to  warrant  great  inconvenience  or  expense  in  obtain- 
ing it. 

23.  Maximum  Velocity  in  Feet  per  Second. 

37.  As  in  items  11  and  17,  this  has  no  direct  bearing  upon 
the  single  test,  but  is  for  use  in  making  comparative  tests  of  differ- 
ent engines  and  for  determination  of  points  of  design. 

24.  Specific  Heat,  Ov. 

38.  Unless  it  is  convenient  to  ascertain  accurately  the  desired 
specific  heat  of  the  gas  used,  no  serious  error  results  from  taking 
the  specific  heat  at  constant  volume  the  same  as  for  air;  namely, 
Ov  =  .1691. 

25.   Cubic  Feet  of  Standard  Gas  per  Hour  (60  Degrees  Fahr.,  14.7 

1  *o unds  Pressure) . 

39.  The  general  standard  recommended  seems  to  indicate  for 
" Standard  Gas"  the  conditions  given;  namely,  a  temperature  of  60 
degrees  Fahr.  and  a  pressure  corresponding  to  the  usual  atmos- 
pheric pressure.     It  is  hardly  necessary  to  make  corrections  for 
barometric  readings,  as  the  total  possible  variation  is  slight,  and 
considering  all  other  sources  of  error  it  is  a  question  whether  this 
supposed  degree  of  refinement  adds  to  the  accuracy  of  the  results. 

Atmospheric  pressure  will  then  be  understood  to  mean  as  in- 
dicated, 14.7  pounds  per  square  inch. 

40.  The  pressure  shown  by  the  manometer  attached  to  the  gas 
pipe  might  also  be  neglected  in  making  the  computations,  as  its 
effect  upon  the  result  is  hardly  perceptible.    It  has,  however,  been 
considered  in  the  illustrative  problems,  the  value  having  been  re- 
corded in  the  log  of  the  test,  thus  adding  no  labor  to  the  computa- 
tions.   It  may  be  of  interest  to  note  that  the  total  effect  of  neglect- 


WORKING   DETAILS  OF  A   GAS  ENGINE  TEST. 


ing  both  the  changes  in  barometric  conditions  and  in  the  pressures 
shown  by  gas  mains,  when  these  changes  are  taken  at  a  maximum, 
is  less  than  one-half  of  One  per  cent,  of  the  number  of  cubic  feet 
per  hour. 


Data  Given. 

Tog  =.  cu.  ft.  of  gas  per  hour  at  tg  °  F. 
Tg  =  absolute  temp,  of  gas  =  t,  °  +  459°. 
pg  —  pressure  under  which  gas  is  flow- 
ing. 
=  14.7    Ibs.  +  pressure     shown     by 

manometer. 
T.  =  60°  +  459°  =  519°     F.,     absolute 

temp,  of  standard  gas. 
Po  =  atmospheric  pressure. 
=  14.7  Ibs.  per  sq.  in. 

To  Find— 
v,  =  cu.  ft.  standard  gas  per  hour. 

Examples. 
"A"  Run  No.  6: 
vg  =  157.5  cu.  ft. 
Tg  =  86°  +  459°  =  545°. 
pg  =  14  7  +  .1  =  14.8  Ibs.  per  sq.  in. 
"B"  Run  No.  6: 
v,  =  91.5  cu.  ft. 
Tg  =  87°  +  459°  =  546°. 
pg  —  14.7  +  .1  =  14.8  Ibs.  per  sq.  in. 


Solution. 


>  P,  r, 


..  ft. 


VALVE    INDEX    HEADING. 

26.   Gas.    27.  Air. 

41.  This  refers  to  the  setting  of  the  graduated  inlet  valves,  and 
has  no  direct  bearing  on  the  single  test,  but  is  of  value  in  making 
comparative  tests. 

28.    Value  of  n  in  PVn  —  I\  V™  for  Expansion  Curve. 

42.  At  this  point  in  the  analysis,  more  or  less  difficulty  is  likely 
to    be    encountered.      The    necessity    of    carefully    working   out 
this  value  of  n  for  each  card  may  not  at  first  seem  apparent, 
but  slight  investigation  shows  it  to  be  of  great  importance. 

It  is  not  unnatural  to  assume  that  the  expansion  curve  and  the 
compression  curve,  as  given  by  the  indicator  card,  follow  very 
closely  the*  adiabatic  law. 


24 


WORKING   DETAILS   OF   A   GAS   ENGINE   TEST. 


Working  upon  this  supposition  leads  in  many  cases  to  a  network 
of  difficulties,  from  which  it  is  not  easy  to  free  one's  self.  For 
example,  a  case  that  came  to  the  attention  of  the  writer  was  as 
follows :  In  making  a  preliminary  test,  owing  to  the  fact  that  it 
was  inconvenient  to  determine  the  exact  clearance  volume  of  the 
engine,  instructions  were  given  to  work  out  the  clearance  from 
the  indicator  card.  The  method  is  quickly  shown  by  the  following 
deductions  and  reference  to  the  card  shown  in  Fig.  2: 


FIG.  2 


43.  ^Let  Vi  =  clearance  volume  of  cylinder. 
vz  =  total  volume  of  cylinder. 

po  —atmospheric  pressure  =  14.7poundsper  square  in. 
pb  =  pressure  at  compression,  from  card. 
I  =  length  of  stroke  in  feet  or  inches,  as  desired. 
x  =  length  of  clearance  in  feet  or  inches,  as  desired. 
It  appeared  a  simple  matter  to  solve  for  x  in  the  following  for- 


mulas :    J_5  —  (  _2 
i>i 


or 


=  -2    which 


readilv    reduces    to 


14.7 


2»  V  - 


x  +  I 


on   the  assumption   that  n  for  the  compression 


curve  was  1.41  or  —  =  71 
n 

This  gave  an  excessively  large  clearance  volume,  and  the  values 
of  n  worked  out  for  the  expansion  curve  varied  greatly,  but  the 
best  value  seemed  to  be  about  1.7,  although  the  necessity  of  care- 
fully determining  the  value  of  this  exponent  for  each  card  was  at 
once  apparent. 


WORKING  DETAILS  OF  A  GAS  ENGINE  TEST. 


25 


Maximum  temperatures  computed  on  the  basis  of  the  value  of 
n  above  proved  to  be  in  the  neighborhood  of  4,00.0  degrees  Fahr. 
This  surprisingly  large  value  of  n,  together  with  the  excessively 
high  temperatures,  led  at  once  to  a  careful  study  of  the  problem, 
for  it  was  apparent  that  no  assumptions  regarding  the  laws  of  ex- 
pansion could  safely  be  made.  The  clearance  volume  was  at  once 
determined  by  the  usual  method  of  filling  the  space  with  water. 
It  may  be  well  here  to  emphasize  the  necessity  of  great  care  in 
releasing  all  air  from  this  clearance  space  as  the  water-  is 
poured  in. 

44.  The  values  of  n  now  deduced  from  the  expansion  curve  for 


FIG.  3 


the  diagrams  taken  from  this  particular  engine  showed  for  portions 
of  the  curve  values  as  surprisingly  low  as  those  first  determined 
were  high.  It  was  found  that  this,  exponent  varied  greatly  in  dif- 
ferent parts  of  the  curve  for  the  diagrams  taken  from  this  engine, 
but  no  satisfactory  law  of  variation  could  be  determined.  With  the 
high  pressure  spring  used  in  the  indicator  it  was  very  difficult  to 
obtain  accurate  values  from  the  cards  secured. 

45.  With  a  240-lb.  spring,  which  was  the  one  used,  each  .01 
of  an  inch  in  vertical  measurement  corresponds  to  2. 41bs.  pressure, 
and  errors  resulting  from  irregularities  in  the  curve,  variations 
in  the  width  of  line,  and  mistakes  in  observation  render  it  almost 
impossible  to  work  with  the  degree  of  accuracy  desired.  In  Fig.  3 
is  showrn  one  of  the  cards  taken  in  making  test  "  A."  The  upper 
dotted  curve  represents  isothermal  expansion  and  the  lower  dotted 
curve  adiabatic  expansion. 

It  is  seen  at  a  glance  that  early  in  the  expansion  the  full  line 
follows  very  closely  the  adiabatic  curve  and  then  approaches  nearer 
and  nearer  the  isothermal  as  the  expansion  continues.  The  value 
of  n  that  has  been  chosen  for  recording  in  item  28  is  the  value 


26 


WORKING   DETAILS   OF   A   GAS  ENGINE   TEST. 


found  for  the  latter  par£of  the  expansion,  as  this  value  is  the  one 
most  needed  in  computations  that  follow.  Owing  to  the  fluctu- 
ations in  many  curves  near  the  beginning  of  expansion,  it  has  been 


Fernald 


FIG.  4. 


found  extremely  difficult  to  obtain  values  that  could  be  regarded 
as  reliable  for  the  pressures  desired. 

46.  The  card  shown  in  Fig.  4  was  taken  during  test  "  B,"  and 
although  the  expansion  curve  seems  to  follow  the  adiabatic  more 
closely  than  in  Fig.  3,  yet  there  is  considerable  variation  even  in 
this  case. 

Repeated  calculations  showed  the  best  value  of  n  for  the  expan- 


Fernald 


FIG.  5 


sion  curve  for  the  cards  of  test  "  A  "  to  be  1.14  and  for  test  "  B  " 
1.21  or  1.20. 

The  mathematical  work  involved  in  obtaining  n  is  explained 
below : 


WORKING   DETAILS   OF  A   GAS   ENGINE   TEST. 


27 


Data  Given. 

Any  corresponding  values  of  pressure 
and  volume  obtained  from  the  indicator 
card.  Great  care  should  be  exercised  in 
theselection  of  these  points  if  the  equation 
of  the  expansion  curve  is  found  to  vary 
for  different  portions  of  the  curve.  All 
measurements  must,  of  course,  be  made 
from  the  zero  of  volumes  and  zero  of 
pressures. 

Vi  =  some  assumed  volume. 
P!  =  pressure  corresponding  to  Vt. 
F2  =  another  assumed  volume. 
Pa  =  pressure  corresponding  to  F2. 

Examples. 

"A"  Run  No.  6  (For  this  problem 
the  values  of  P  and  V  are  selected  as 
shown  in  Fig.  5)  : 

Fa  =    62         Pi  =  141 
F2  =  12.2         P2  =    65 


B  "  Run  No.  6  : 

F,  =  5  Pi  =  1(8 

V,=8  P2  =    61 


Solution . 


P! 


71    = 


log.  P.  -  log.  P, 
-  log.  F2  -  log.  F, 


log.  Px  =  2.14922 
log.  P2  =  1.81291 

.33631 


log.  Fa  = 

log.  Fi  =  0.79239 

.29397 


_  .smi_  _ 

~  .29397  ~ 
Solving  by  the  first  formula, 


shortens  the  work  if  a  slide  rule  is  used 
^i  =  ^=  1.77,  log.  =0.24797 

Z?  ^  ?  =  1.6,  log.  =  0.20412 
K  j        5 


.24797 
.20412 


=  1.21 


47.  The  following  values  of  n  were  worked  out  with  great  care 
from  a  series  of  volumes  and  corresponding  pressures,  and  show 
the  fluctuations  to  which  this  calculation  is  subject.  The  values 
are  arranged  as  derived  in  regular  order  from  left  to  right,  but  do 
not  include  values  for  very  small  volumes,  as  the  variations  in 
pressure  were  too  great  to  enable  any  reliable  readings.  As  de- 
rived from  the  card  selected  n  =  1.21,1.12,1.14, 1.16,  1.13,  1.135, 
1.12,  1.10,  1.10  1.12,  1.15,  1.15,  1.15  1.14,  1.16,  1.13. 

A  variation  of  a  single  pound  in  the  pressure,  or,  in  some  cases, 
of  one-half  pound,  determines  the  accuracy  of  the  deduction,  but 
•with  such  high  pressure  springs  this  degree  of  refinement  is  im- 
possible. It  was  noted  in  several  cases  that  the  value  of  n  for  the 


28  WORKING  DETAILS   OF  A   GAS  ENGINE  TEST. 

compression  curve  was  slightly  higher  than  for  the  expansion 
curve. 

A  simple  method  of  ascertaining  whether  this  exponent  is  the 
same  for  corresponding  compression  and  expansion  curves  is  as 
follows : 

48.  Locate  a  series  of  different  volumes  upon  the  card  in  ques- 
tion and  determine  the  corresponding  pressures  for  both  the  com- 
pression and  expansion  curves.  If  the  ratio  of  the  corresponding 
pressures  of  the  two  curves  remains  constant,  the  exponents  for 
the  equations  of  the  two  curves  will  be  found  to  be  identical. 

Let  Fj  and  V.2  =  two  volumes  chosen,  as  in  Fig.  5.  For  the  ex- 
pansion curve  the  two  pressures  =  Pl  and  P2  and  for  the  com- 
pression curve  the  pressures  corresponding  to  the  same  volumes  = 
Ps  and  P4.  Let  x  be  the  exponent  in  the  equation  of  the  expan- 
sion curve,  viz :  Pl  Vf  —  P2  V2X  and  let  y  be  the  corresponding- 
exponent  for  the  compression  curve,  or  P9  V?  =  P±  V/ 

By  division  y    Y^  —  P*— M    If  now  the  exponents  for  the  two 

•*  8       '1  *4       *  2 

curves  be  the  same,  i.  e.,  ify  =  x  then  ^_^L  =  ^_p*  or  ^  =  P\ 

*8      M  ^4      '2  •*  8         -*4 


MIXTURE. 

29.  Temperature,  Degrees  Falir. 

49.  One  of  the  longest  deductions,  as  well  as  one  of  the  most 
difficult,  but  at  the  same  time  of  great  importance,  is  that  of  ob- 
taining the  temperature  of  the  mixture  in  the  cylinder,  composed 
of  air,  gas,  and  exhaust  gases,  or  neutrals,  as  the  last  are  some- 
times called.  The  problem  involves  the  larger  portion  of  all  the 
readings  made  during  the  test,  as  well  as  the  careful  determination 
of  the  temperature  of  the  exhaust  gases. 

The  mixture  passes  through  a  wide  range  of  temperatures,  and 
the  only  one  that  can  be  determined  is  that  of  the  exhaust.  This 
has  proved  to  be  of  such  great  importance  and  so  little  seems  to 
be  known  regarding  the  determination  of  this  factor,  that  much 
of  the  time  devoted  to  the  subject  of  gas  engine  testing  was  given 
to  the  solution  of  this  problem. 

Very  few  methods  for  measuring  this  temperature  seem  to  exist, 
and  these  are  either  too  inaccurate  to  be  of  any  value,  or  in  cases 
where  the  results  seem  to  indicate  accuracy,  the  method  is  too 


WOKKING   DETAILS   OF   A   GAS   ENGINE   TEST. 


29 


complicated  or  the  apparatus  too  expensive  for  use  under  ordinary 
circumstances. 

50.  Even  the  committee  appointed  by  the  Society  to  "Standard- 
ize a  System  of  Testing  Steam  Engines  "  avoids  the  question  en- 
tirely. This  committee  speaks  of  the  "  observed  temperature  of 
the  exhaust  gases/'  but  in  no  way  is  any  intimation  given  of  a 
method  of  observation. 

A  simple  device  for  determining  these  temperatures  seems  so 
necessary  that  it  is  deemed  wise  to  give  a  complete  description  of 
the  apparatus  used  by  the  writer,  in  a  separate  paper  entitled,  "A 
Method  of  Determining  the  Temperatures  of  Exhaust  Gases/7  and 
to  be  presented  as  paper  ISTo.  0932  at  this  meeting. 

To  avoid  confusion,  the  computations  for  determining  the  tem- 
perature of  the  mixture  will  be  divided  into  two  parts. 


PART  I. 

51.  To  determine  the  combined  volumes  of  air  and  gas  per 
stroke  and  the  temperature  of  the  same : 

Case  1.  When  the  temperatures  of  the  incoming  air  and  gas 
are  equal: 


Data  Given. 
Mins.  =  No.  minutes  in  time  interval. 

item  19 
£  =  gas  per  min.  = 


item  13 
«  =  air  per  min.    =  -^7^- 

Ti  =  absolute  temp.  gas. 
=  T\  absolute  temp.  air. 
=  item.  21  or  15  4-  459°. 
Ex.  P.  M.  =  explosions  p.  min.  —  item  6. 
R.  P.  M.  =  re  volutions  p.  min.  =  item  4. 
Ms.  P.  M.  =•  explosions  missed  per  min. 
=  |  R.  P.  M.  -  Ex.  P.  M.  for 
single  cylinder  four-cycle 
engine. 

To  Find— 

•D'  =  cu.  ft.  gas  per  explosion  at  Ti. 
•v"  =  cu.  ft.  air  per  explosion  at  1\. 
T^  =  absolute  temperature  in  F.°  re- 

sulting from  combining  air  and 

gas  =  Z\  =  2>. 
vaff  —  combined  vol.  in  cu.   ft.  of  air 

and  gas  per  explosion  at  T^. 


Solution. 


Ex.  P.  M. 


\R.  P.  M.] 


Since 


Tag  = 


30 


WORKING   DETAILS   OF   A   GAS   ENGINE   TEST. 


A  "  Run  No.  6: 

26.25 
9  = 


10 

194 
10 


=  2.625cu.  ft. 


=  19.4cu.  ft. 


Ti  =  T*  =  86°  +  4o9°  =  545C 
Ex.  P.  M.  =  133.9. 
R.  P.  M.  =267.9. 
Ms.  P.  M.  =  0. 

B"  Run  No.  6: 
15.25 


9  = 


a  = 


10 

125.0 
10 


=  1.586  en.  ft. 


=  12.5  QU.  ft. 


2\  =  2\  =  87°  +  459°  =  546C 
Ex.  P.  M.  =  93.4. 
R.  P.  M.  =301.2. 
Ms.  P.  M.  =57.2. 


v  "'WH  =  -°196cu- ft- 

19.4  -  .0196  x  0 


And  since 

Vaa   —   V 


133.9 

Tag  =  i\  =  r,, 


=  .  145cu.ft. 


v"  =    1646  cu.  ft. 


•= =.««•««. « 

.18. 5-. 0163  x  57  2 
150.6 


=  .<>769  cu.  ft. 


And  since     Tag  =  7\  =  7'a  =  546°, 

<Kaa=  v'  +  v"  —  .09:]'*  cu.  ft. 


Case  2.  When  the  temperatures  of  the  incoming  air  and  gas 
are  different: 


Data  Given. 
Mins.  =  No.  minutes  in  time  interval. 

.  <      item  19 
<7  =  gas  per  mm.  =  — 

mins. 

item  13 
a  =  air  per  mm.  =  — 

mins. 

T\  =  absolute  temp,  air  in  F.° 

=  item  15  +  459°. 
T9  =  absolute  temp,  gas  in  F.° 

=  item  21  +  459°. 
Ex.  P.  M.  •=  explosions    per    minute  = 

item  6. 
R.  P.  M.  =  revolutions   per  minute  = 

item  4. 

Ms.  P.  M.  =  explosions  missed  per  min. 
=  i  R.  P.  M.  -  Ex.  P.  M.  for 
single  cylinder  four-cycle 
engine. 

Wi  --  "wgt.  percu.  ft.  air  at  T\  =  item  16. 
Wo  =  wgt.  per    cu.  ft.  air  at  32°  F.  = 

.0807  Ib. 
To  =  absolute   temp,   corresponding    to 

32°  F.  =  491°. 
v'  =  cu.  ft.  gas  per  explosion  -\       as 

at  Tt  I    found 

u"  =  cu.  ft.  air  per  explosion  \    under 
at  Ti  J  Case  1. 


Solution. 

The  general  equation  from  which 
T^  can  be  computed  is 

cp  (1\  -  Tag}  wa  =  cp  (T^  -  7\)  t/v 

It  is  now  necessary  to  find  wa  and  wff. 

If  it  is  not  convenient  to  obtain  the 
weight  of  gas  per  cubic  foot,  the  best 
that  can  be  done  is  to  take  the  weight 
of  gas  the  same  as  that  of  air  at  the 
same  temperature.  The  error  involved 
by  so  doing  is  not  serious. 

7'0 


Then 


Wy    =  W0 


xv 

X      V 


Tag    can    now   be    computed    from   the 
equation  above. 


v     —v    -~ 


1\ 


ag  =  V       4-    V 


WORKING  DETAILS   OF  A   GAS  ENGINE  TEST. 


31 


Cp  —  specific  heat    of    air  at    constant 
pressure. 

To  Find— 

w?  =  wgt.  cu.  ft.  gas  at  TV 
wa  —  wgt.  of  air  per  explosion  at  2\. 
wg  =  wgt.  of  gas  per  explosion  at  TV 
T^  =  absolute   temp,   in   F.°  resulting 

from  combining  air  at   7\  and 

gas  at  TV 

v'"  —  cu.  ft.  gas  per  explosion  at  Tag. 
v""  =  cu.  ft.  air  per  explosion  at  T^. 
Vag  =  combined   vol.  in   cu.  ft.    of   air 

and  gas.  per  explosion  at  T^. 


PART  II. 

52.  The  combined  volumes  of  air  and  gas  used  per  explosion, 
together  with  the  temperature  of  the  same,  having  been  computed 
as  indicated  in  Part  I.  of  this  section,  the  problem  is  now  to  deter- 
mine the  temperature  of  the  final  mixture  in  the  cylinder  after  the 
air  and  gas  have  united  with  the  exhaust  gases  in  the  clearance 
space — unless  the  engine  is  of  the  scavenging  type. 

It  is^to  be  noticed  that  if  the  governor  is  of  the  hit  or  miss  type, 
the  exhaust  stroke  following  a  miss  corresponds  to  a  scavenging 
stroke. 


Data  Given. 

Assume  the  weight  of  the  final  mix- 
ture equal  to  the  weight  of  air  at  i  he  same  j 
temperature.     Assume  the  specific  heats 
of  the  different  mixtures  the  same  as  for 
air. 

w0  =  weight  cu.  ft.  air  at  32°  F.  = 
.0807  Ib. 

To  —  absolute  temp,  corresponding  to 
32°  F.  =  491°. 

Gp  =  specific  beat  air  at  constant  pres- 
sure. 

=  specific  heat  air  and  gas  at  con- 
stant pressure. 

=  specific   heat    final    mixture   at 
constant  pressure. 

Tag=  absolute  temp,  of  air  and  gas 
entering  cylinder  as  computed 
in  Part  I. 


Solution. 


T 


Tm  can   now  be  computed   from  the 
equation 

cf  (Tm  -  T.,)  wag  =  cp  (Tt  -Tm)wt 


Ta  wa 


Te  w, 


WORKING  DETAILS   OF   A  GAS   ENGINE  TEST. 


'Dag  —  cu.  ft.  air  and  gas  at  Tag  as  com 

puted  in  Part  I. 
Te  =  absolute  tenip.  exhaust  gases  at 

atmospheric  pressure. 
=  temp,  observed  and  recorded  in 

item  14  of  log  4-  459°. 
vb  =  vol.  of  clearance  in  cu.  ft. 

To  Find — 
Ws  =  weight  cu.  ft.  of  air  and  gas  at 

av 

?r4  =  weight  cu.  ft.  of  exhaust  gases 

at  T.. 

wag  =  weight  of  air  and  gas  per  ex- 
plosion at  Tag. 

w(  =  weight  of  exhaust  gases  per  ex- 
plosion at  Te. 
Tm  =  absolute  temp,  of  final  mixture 

in  cylinder. 
Tm  -  459°  =  F.°  as  in  item  29. 

Examples. 
"A"  Kun  No.  6: 
wo  =  .0807  Ib. 
To  =  32°  +  459°  =491°. 
T   =  rl\  =  T2  =  86°  +  459°  =  545°. 
^=.1646    cu.    ft.    as    computed    in 

Part  I. 

T  =  180°  +  459°  =  639°  by  observa- 
tion. 
vb  =  .055  cu.  ft   by  measurement. 


"B"  Run  No.  6  : 

w0  =  .0807  Ib. 

T0  =  32°  +  459°  =  491°. 

Tag-  87°  +  459°  =  546°. 

Vag  =  .0932    cu.    ft.    as    computed    in 
Part  I. 

T  =188°  +  459°  —  647°  by  observa- 
tion. 
V6  =  .037  cu.  ft.  by  measurement. 


4Q1 

=  .0807—  =  .0727  Ib. 
o45 


4Q1 

~ 

boy 


=  .0621  Ib. 


wag  =  .0727  x  .1646  =  .0120  Ib. 
we  =  .0621  x  .055  =  .00342  Ib. 

(Tm  -  545)  .012  =  (639  -  Tm)  .00342 
.01542  Tm  =  8.72 
Tm  =  565° 
565°  -  459°  =  106°  F. 

4Q1 

=  .0725  Ib. 


4Q1 

w4  =  .0807^  =  .0612  Ib. 
647 

wag  =  .0725  x  .0932  =  .00676  Ib. 
we  =  .0612  x  .037  =  .00226  Ib. 

(Tm  -  546)  .00076  =  (647  -  Tm)  .00226 
.00902  7'm  =  5.15 
Tm  =  572° 

5720  _  4590  _  113o  F 


53. 


30.    Weight  per  Cubic  Foot. 
Data  Given. 


'Co  =  weight   cu.  ft.   air    at   32°   F.  = 

.0807. 
r0  =  absolute  temp,   corresponding   to 

32°  F.  =  491°. 
rm  =  absolute    temp,    of    mixture    as 

computed  in  29. 


Solution. 

To 


WORKING   DETAILS  OF  A  GAS  ENGINE  TEST. 


33 


•To  Find— 
J5  —  weight  cu.  ft.  of  mixture  at  Tm. 

Examples. 
"A"  Run  No.  6  : 

Tm  =  565°  from  29. 

"B"  Run  No.  6  : 

Tm  =  572°  from  29. 


=  .0807^  =  .  0701  Ib. 
o65 


=  .0807        =  .0692  Ib. 

0  I  '  4 


31.  Maximum  Velocity,  Feet  per  Second. 

54.  This  velocity  refers  strictly  to  the  rate  of  flow  of  the  enter- 
ing mixture  of  air  and  gas  and  not  to  the  final  mixture  in  the  cyl- 


FIG.  6. 


inder.  As  in  columns  11,  17,  23,  this  maximum  velocity  is  for  use 
in  making  comparative  tests  only,  and  for  determining  points  of 
design. 


PKESSUEE    FROM    INDICATOR   CARDS. 

55.  The  indicator  card  bears  such  an  important  relation  to  the 
test  that  great  care  should  be  taken  to  have  the  reducing  motion, 
indicator,  and  all  connections  properly  adjusted.  Owing  to  the  ex- 


34 


WORKING    DETAILS   OF   A   GAS   ENGINE   TEST. 


treme  maximum  pressure  resulting  from  the  explosion,  the  ordi- 
nary steam  engine  indicator  is  far  too  delicate  for  service.     A 


FIG.  7. 


special  gas  engine  indicator  with  a  small  piston,  strong  spring, 
strengthened  pencil  arm  and  carefully  adjusted  pin  connections  is 
very  necessary.  It  is  well  at  all  times  to  keep  the  pipe  leading  to 


WORKING  DETAILS  OF  A  GAS  ENGINE  TEST.  35 

the  indicator  packed  with  cotton  waste  saturated  frequently  with 
water,  to  prevent  the  temperature  of  the  indicator  from  becoming 
excessive  and  thus  rendering  it  unreliable.  When  it  can  be  easily 
done  it  is  an  excellent  plan  to  jacket  this  connection. 

Care  should  always  be  taken  to  record  on  the  log  sheet  the 
scale  of  the  spring*  used.  Never  trust  to  memory  for  this  or  any 
other  fact. 

When  the  compression  cylinder  is  independent,  the  scale  of  the 
spring  used  for  the  cards  taken  from  this  cylinder  should  also  be 
recorded  on  the  log  sheet,  and  the  card  so  taken  should  be  reduced 
to  the  same  scale  and  combined  with  the  power  card. 

For  convenience  in  making  this  combination  care  should  be  ex- 


FIG.8 

ercised  in  adjusting  the  reducing  motion  to  insure  the  same  length 
of  card  in  both  cases. 

56.  The  reducing  motion  may  be  any  one  of  the  forms  usually 
constructed  for  such  purposes,  provided  it  can  be  readily  attached. 

The  lack  of  a  cross-head  and  the  enclosed  crank,  case  on  the 
modern  gas  engine  prevent  the  use  of  some  reducing  motions. 
The  forms  shown  have  been  used  with  perfect  satisfaction  upon  the 
engines  tested  at  Columbia,  that  shown  in  Fig.  6,  for  horizontal 
engines,  and  that  in  Fig.  7  for  vertical.  They  are  especially 
recommended  for  cheapness  and  for  the  ease  with  which  they  can 
be  constructed  on  the  grounds. 

The  utmost  care  should  be  exercised  in  adjusting  the  reducing 
motion.  It  is  not  sufficiently  accurate  to  regulate  merely  by  the 
eye,  but  sample  cards  should  be  taken  and  adjustments  made  until 
the  motion  is  correct. 

57.  Fig.  8  shows  the  result  when  the  true  position  of  the  reducing 
motion  is  seriously  disturbed.     The  engine  appears  to  continue 
compressing  long  after  the  piston  has  started  toward  the  crank 


36 


WORKING  DETAILS  OF  A  GAS   ENGINE  TEST. 


end  of  the  cylinder,  the  maximum  compression  pressure  being 
shown  at  8,  at  which  point  the  ignition  takes  place.  The  series  of 
explosions  which  follow  in  rapid  succession  when  the  ignition  is 


FIG.  9 


Feniald 


early,  as  is  the  case  in  this  instance,  appear  seriously  distorted,  con- 
tinuing apparently  through  the  greater  part  of  the  stroke,  an  effect 
produced  by  the  relatively  high  speed  of  the  indicator  drum.  With 


FIG.  10 


Fernald 


a  card  so  seriously  distorted,  the  error  is  quickly  perceived,  but 
when  the  error  is  as  shown  in  Fig.  9,  the  difficulty  is  not  quite 
as  apparent. 

A  casual  glance  might  lead  one  to  suppose  this  form  of  card 


FIG.  11 


Fernald 


due  to  late  ignition,  but  closer  examination  will  show  the  compres- 
sion pressure  to  be  steadily  rising  to  the  point  8.  This  indicates 
that  the  reducing  motion  is  still  incorrectly  adjusted. 


WORKING   DETAILS   OF  A  GAS  ENGINE   TEST.  37 

When  a  similar  effect  is  produced  by  late  ignition  only  and  the 
reducing  motion  is  properly  set,  the  line  from  B  to  8  is  horizontal 
or  even  depressed,  as  shown  in  Figs.  10  and  11. 

58.  Fig.  12  shows  a  case  that  is  approaching  the  limiting  posi- 
tion of  the  reducing  motion,  but  close  scrutiny  shows  the  com- 
pression to  continue  slightly  after  the  engine  has  passed  its  dead 


FIG.  12 


Fernald 


centre.  The  early  ignition  shown  in  Fig.  12  tends  to  conceal  the 
fault  due  to  the  reducing  motion,  and  in  cases  where  the  ignition 
is  premature  great  care  should  be  taken  to  secure  the  proper  regu- 
lation before  ignition  is  set  too  early.  , 

In  Fig.  13  is  shown  the  typical  card  with  early  ignition  and 
the  reducing  motion  properly  set  so  that  the  maximum  compression 
as  shown  by  the  card  corresponds  to  the  position  of  the  inner  dead- 
centre  of  the  engine. 


FIG.  13 


Fernald 


Errors  of  the  kind  just  described,  although  apparently  slight 
in  the  limiting  cases,  should  be  guarded  against,  as  the  deductions 
of  the  entire  test  may  be  seriously  affected  by  such  oversights. 

To  insure  accuracy  it  is  better  to  establish  the  line  L  C,  Fig.  14, 


38  WORKING  DETAILS  OF  A  GAS  ENGINE  TEST. 

by  allowing  the  indicator  drum  to  remain  stationary  while  the  indi- 
cator cock  is  opened  and  the  pencil  moved  up  and  down,  than 
simply  to  draw  L  C  at  rigHt  angles  to  the  atmospheric  line.  The 
lines  of  zero  volume  and  zero  pressure  can  then  be  drawn  parallel 
to  L  C  and  the  atmospheric  line  respectively. 

32.  Pressure  at  End  of  Compression. 

59.  Eeferring  to  the   diagram   (Fig.    14),   the   absolute   com- 
pression pressure  is  represented  by  the  distance  LB,  measured 
from  the  line  of  zero  pressures. 

33.  Maximum  Pressure,  or  Pressure  at  the  Beginning  of 
Expansion. 

60.  Some  care  is  necessary  in  determining  this  value  in  cases 
where  the  diagram  shows  a  series  of  explosive  waves.  In  Fig.  14 


FIG.  14 


the  distance  measured  from  the  zero  pressure  line  to  the  point  C 
is  easily  determined  as  the  maximum  pressure,  but  in  cases  like 
Fig.  15  the  possibility  of  error  is  much  greater. 

By  marking  the  centre  points  of  the  series  of  explosion  peaks 
and  continuing  the  expansion  line  from  some  lower  point  in  the 
curve  through  these  points,  a  fairly  accurate  determination  of  the 
maximum  pressure  may  be  made. 

If  the  value  of  n  determined  in  28  be  regarded  as  accurate,  a 
rery  good  check  may  be  had  upon  the  maximum  pressure  obtained 
graphically,  by  computing  the  pressure  from  the  equation  of  the 
curve. 


WOEKING  DETAILS  OF  A  GAS  ENGINE  TEST. 


39 


34.  Pressure  at  End  of  Expansion. 

61.  The  determination  of  the  end  of  expansion,  or  point  of  re- 
lease, is  often  attended  by  some  difficulty,  as  the  point  is  not 
marked  by  any  sudden  change  in  the  direction  of  the  expansion 
curve,  but  is  at  the  point  of  inflexion,  D  (Fig.  15).    As  in  the  other 
cases  the  pressure  is  measured  from  the  zero  lines  of  pressures. 

35.  Pressure  if  Expansion  were  Carried  to  End  of  Stroke. 

62.  This  value  is  readily  obtained  from  the  equation  of  the  ex- 
pansion curve,  the  value  of  the  exponent  n  having  been  computed 
in  28.     If  the  expansion  were  thus  continued  it  would  give  the 
point  H,  as  shown  in  Fig.  15.    The  pressure  corresponding  to  the 
point  H  is  deduced  as  follows : 


Data  Given. 

V\  =  volume  at  some  point  of  the  card. 
Pi  =  pressure  corresponding  to  V\. 
n   —  value  deduced  in  28. 
F3  =  total  volume  of  cylinder. 

To  Find— 

I\  =  pressure    corresponding    to    F2  ; 
i.  e. ,  if  expansion  continued  to  H. 


Examples. 
"A"  Run  No.  6  : 
Vi  —  12.2  for  one  point  of  card. 
Pi  =  60  pounds  pressure  corresponding 

to  Fi. 

//,  =1.14  from  item  "28. 
F2  =  15.9  for  total  volume  of  cylinder. 


"B"  Run  No.  6  : 
Fi  =  8  for  one  point  of  card. 
Pi  =  61  pounds  pressure  corresponding 

to  Fi. 

n  =1.21  from  item  28. 
Fa  =  11.25  for  total  volume  of  cylinder. 


Solution. 
F,"  =  P2  F2" 


log.  P2  =  log.  P,  +  n  leg.  - 

The  volumes  being  used  as  a  ratio, 
the  piston  area  may  be  omitted,  the  ratio 
of  lengths  being  the  same  as  the  ratio 
of  volumes,  as  is  customary  in  working 
with  indicator  cards. 


=  «©' 


1.14  log.          =  9.86885  -10 
10." 

log.   65    =  1.81291 

log.  P2  =  1.68176 

P2   =48 


(ft    \  l-ai 
nW 


1.21  log.  _L_  =  9.82076  -  10 

log.    61    =  1.78533 

log.     P2   =  1.60609 

Pa  =  40.5 


40 


WORKING  DETAILS  OF  A  GAS  ENGINE  TEST. 


.36.  Mean  Effective  Pressure. 

63.  It  is  necessary  to  determine  the  area  of  the  diagram, 
and  for  this  purpose  the  planimeter  should  be  used,  although  other 
methods  will  answer,  but  are  very  tedious  and  not  as  accurate.  The 


Fernald 


FIG.  15 


length  of  the  diagram  is  determined  by  the  lines  LM  and  RW 
(Fig.  15),  and  is  equal  to  LR. 

The  area  in  square  inches  divided  by  the  length  of  the  diagram 
in  inches,  multiplied  by  the  scale  of  the  spring  used,  will  give  the 
mean  effective  pressure  in  pounds  per  square  inch. 


Data  Owen. 

A  =  area  diagram,  sq.  ins. 
L  =  length  diagram,  ins. 
8  =  scale  of  spring  used. 

To  Find— 
M.  E.  P.  —  mean  effective  pressure. 

Examples. 
"  A  "  Run  No.  6  : 

A  =    .84  sq.  ins. 

L  =  3.04  ins. 

8  =  240  Ibs.  per  inch  height. 

"B"  Run  No.  6  : 

A  =    .65  sq.  ins. 

L  =2.76  ins. 

8  =  240  Ibs.  per  inch  height. 

EXHAUST. 

37.   Temperature,  Degrees  Fahr. 

64.  The  subject  of  exhaust  temperatures  has  occasioned  much 
discussion  since  the  advent  of  gas  engines,  but,  as  far  as  the  writer 


Solution. 


M.  E.P.  =  ~ 


M.  E.  P.  =          240  =  66.3  Ibs.  per  sq.  in. 


M.  E.P.  =          240  =  56.5 Ibs.  persq.  in. 


WORKING  DETAILS  OF  A  GAS  ENGINE  TEST.  41 

is  informed,  very  few  methods  have  been  devised  for  securing 
even  an  approximation  to  the  correct  temperatures,  and  even 
these  devices  seem  too  complicated  or  too  expensive  for  ordinary 
use. 

Until  recently  there  seems  to  have  been  little  or  no  comprehen- 
sion of  the  real  temperatures  of  these  -exhaust  gases,  and  to-day, 
even  when  an  appreciation  of  the  high  range  of  temperatures  is  had, 
there  seems  to  be  a  feeling  that  some  slight  modification  of  the 
design  of  the  engine  will  enable  the  inventor  to  save  this  excessive 
waste,  and  thus  to  secure  f or,himself  the  fortune  that  would  result 
from  the  invention  of  engines  showing  a  higher  efficiency.  In  the 
writer's  opinion  this  cannot  be  done  with  engines  working  on  the 


Femald  FIG.  16 

Otto  or  Beau  de  Rochas  cycle,  save  by  a  reduction  of  the  final  or 
exhaust  pressure.  It  can  be  easily  shown  that  with  high  pressure 
of  release,  high  exhaust  temperatures  must  follow.  Some  attempts 
have  been  made  to  reduce  this  terminal  pressure  by  compounding 
or  other  means,  and  while  some  degree  of  success  has  been  attained, 
yet  the  results  have  not  been  of  a  nature  to  create 'any  great  en- 
thusiasm, and  this  leads  at  once  to  the  query, "  Is  this  the  best  cycle 
to  use  for  the  most  effective  results? "  It  is  not  within  the  scope 
of  this  paper  to  treat  this  problem,  but  experimental  results  lead 
to  renewed  interest  in  the  paper  read  by  Mr.  Charles  E.  Lucke  at 
the  last  meeting  of  the  Society,  entitled,  "  The  Heat-Engine  Prob- 
lem,'7 in  which  the  possibilities  of  the  different  cycles  are  treated 
in  detail,  leading  to  strong  recommendations  for  non-explosive  en- 
gines. 

65.  The  details  of  apparatus  for  determining  the  temperature 
of  the  exhaust  gases  are  given  in  the  paper  previously  referred  to 
in  paragraph  29,  but  the  method  of  computation  will  be  outlined 
under  the  present  heading. 

Having  determined  the  temperature  of  the  mixture  in  the  cylin- 


WORKING  DETAILS  OF  A  GAS  ENGINE  TEST. 


der  at  atmospheric  pressure,  as  recorded  in  item  29,  the  method 
employed  for  the  present  deduction  is  very  simple: 


Data  Given. 
(See  Fig.  16.) 

pa  =  pressure  at  A  =  atmosph.  pres- 
sure =  14.7  Ibs. 

ph  =  pressure  at  //  =  value  of  item  35. 

Tm  —  absolute  temp,  of  mixture  at  at- 
mot<ph.  pres.  =  item  29  -f  459°. 

.      To  Find— 
Th  =  absolute  temp,  of  exhaust. 

Examples. 
"A"  Run  No.  6: 
pa  =  U.7  Ibs. 
ph  =  48  Ibs. 
Tm  =  106°  +  459°  =  565°. 

"B"  Run  No.  6: 
pa  —  14.7  Ibs. 
pA  =  40.51bs. 
Tm  =  113°  +  459°  =  572°. 


Solution. 
The  volumes  at  A  and  H  being  equal, 


Th  =  565 


48 


=  1,846C 


14.7 

1,846°  -  459°  =  1,387°  F. 


Tk  =  572 


=  1,579 


1,579°  -459°  =  1,120°  F. 


66.  Owing  to  the  throttling  of  the  entering  gases  the  mixture 
in  the  cylinder  is  slightly  below  atmospheric  pressure  at  full  cylin- 
der volume,  but  the  amount  is  not  large  and  is  not  worth  consider- 
ing when  compared  with  the  possible  errors  that  may  occur  in 
obtaining  the  various  pressures  from  the  indicator  card  when  a 
high-pressure  spring  is  used.  The  temperature  at  release  would,  of 
course,  be  considerably  higher  than  that  given  for  the  point  H. 
That  the  exhaust  temperatures  cannot  be  as  low  as  has  been  fre- 
quently supposed,  even  by  recognized  authorities,  is  readily  shown 
by  a  very  brief  calculation : 

For  an  extreme  case  give  both  the  temperature  of  the  mixture 
and  the  pressure  H  very  low  values,  thus  reducing  the  exhaust 
temperature  to  a  minimum. 

Suppose  the  temperature  of  the  mixture  to  be  as  cool  as  the 
atmosphere  on  a  cool  day,  say  60  degrees  Fahr.,  and  take  the  pres- 
sure at  H  as  low  as  35  pounds.  The  resulting  exhaust  temperature 
even  under  these  extreme  conditions,  must  be 

35 
Th  =  519          =  1,234  degrees  or  775  degrees  Fahr. 


WORKING  DETAILS  OF  A  GAS  E 


43 


38.  Maximum  Velocity,  Feet  per  Second. 

67.  As  in  items  11,  17,  23,  31,  this  maximum  velocity  is  for 
use  in  making  comparative  tests  only,  and  for  determining  points 
of  design. 

39.  Specific  Heat,  Cv. 

68.  Unless  the  specific  heat  of  the  exhaust  gases  can  be  readily 
obtained,  the  specific  heat  at  constant  volume  may  be  taken  the 
same  as  for  air,  namely,  Cv  =  .1691. 


RATIOS. 
40.  Air  to  Gas  to  Neutrals. 

69.  By  "  neutrals  "  is  meant  the  products  of  combustion  left 
in  the  cylinder  of  a  non-scavenging  engine  after  exhaust — an 
amount  equal  in  volume  to  that  of  the  clearance  space. 

In  determining  the  proportions  called  for,  the  number  of  cubic 
feet  of  gas  is  taken  as  unity,  and  the  temperature  of  the  gas  is 
taken  as  the  basis  for  the  computation.  The  quantities  of  air 
and  neutrals  must  be  reduced  to  corresponding  amounts  at  this 
temperature. 

The  cubic  feet  of  air  used  in  ten  minutes  or  an  hour  cannot 
be  taken  as  a  basis  of  comparison,  without  modification,  owing  to 
the  misses  of  explosions,  in  which  case  air  is  taken  into  the  cylinder 
without  gas. 


Data  Given. 
T\  —  absolute    temperature    of    air  = 

item  15  +  459°. 
T-2  =  absolute  temperature    of    gas  — 

item  21  +  459°. 

Te  =  absolute  temp,  of  exhaust  gases 
=  item  14  of  log  +  459°. 

at  atmospheric  pressure. 
v '  =  cu.  ft.  gas  per  explosion  at  TI  as 

computed  in  29. 
v  "  =  cu.  ft.  air  per  explosion  at  Ti  as 

computed  in  29. 

ve  =  cu.  ft.  neutrals  per  explosion. 
=  volume  of  clearance  =  t>4. 

To  Find— 

cu.  ft.  air  per  explosion  at  1\. 
cu.  ft.  neutrals  per  explosion  at  I \. 


/Solution. 


v^=TL  ,,T*_ 

v "       Ti  Ti 


Taking  v '  as  the  basis,  i.e.    calling   v' 
unity,  then 


WOKKING  DETAILS  OF  A  GAS  ENGINE  TEST. 


Examples. 
A"  Run  No.  6: 

r,  =  86°  +  459°  =  545°. 
T2  =  86°  +  459°  =  545° 
T.  =  180°  +  459°  =  639°. 
i)'  =  .0196  cu.  ft. 
v"  =  .1450  cu.  ft. 

Ve  =  .0550  CU.  ft. 

B  "  Run  No.  6  : 

Ti  =  87°  +  459°  =  546°. 
T-2  =  87°  +  459°  =  546°. 
Te  =  188°  +  459°  =647°. 
v'  =  .0163cu.  ft. 
v"  =  .0769  cu.  ft. 
ve  =  .0370cu.  ft. 


xix  =  .145^p  =  -145  cu.  ft. 

FJ4K 

vz  =  .055g^=  .0469cu.  ft. 
vx   :«'  :vg  =  7.4  :  1  :  2.4. 

vx  =  .0769  f^  =  .0769  cu.  ft. 
545 

KAK 

vz  =  .037   ~=  .0312cu.  ft. 


41.  /Stroke  to  Expansion. 

TO.  This  ratio  shows  the  regularity  of  the  opening  of  the  ex- 
haust valve,  i.e.,  the  position  in  the  stroke  of  the  point  of  release, 
and  is  equal  to  the  ratio  of  the  full  stroke  to  the  horizontal  projec- 
tion of  the  expansion  curve  taken  to  the  release  point.  In  this 
diagram  shown  in  Fig.  17,  it  is  the  ratio  of  FA  to  FJ. 


FIG.  17 


For  "  A  "  run  No.  6,  this  ratio  was  1.14,  and  for  "  B  "  run  No. 


6,  1.10. 


The  point  of  release  does  not  seem  always  to  correspond  to  the 
point  of  opening  of  the  exhaust  valve.  The  piston  is  moving  rapidly 
and  the  drop  in  pressure  is  not  always  shown  at  once,  especially  if 
the  exhaust  valve  motion  is  not  rigid,  or  if  the  exhaust  valve  is 
of  insufficient  area. 


42.    Volumes  v2  to  v^. 

71.  In  the  diagram  (Fig.  18),  ^  is  proportional  to  the  length 
OZ,  and  represents  the  clearance  volume  of  the  cylinder.     v2  is 


WOKKING  DETAILS  OF  A  GAS   ENGINE   TEST. 


45 


proportional  to  the  length  OR  and  represents  the  full  cylinder 
volume  —  the  clearance  plus  the  stroke.     The  ratio  —  is  therefore 

Vi 

equal  to  7r^.     For  "A"  run  No.  6  this  ratio  was  4.68  and  for 


"B"  run  No.  6,  it  was  5.00. 

43.  Maximum  Pressure  to  Mean  Effective  Pressure. 

This  ratio  shows  the  relation  between  the  pressure  produced 
by  explosion  and  the  true  working  pressure,  and  gives  an  especially 
good  idea  of  the  possibilities  of  different  engines  in  comparative 
tests,  as  well  as  determining  the  possible  degree  of  constancy  in 
this  relation  for  any  single  engine.  It  is  stated  by  some  writers 


FIG.  18 


that  in  practice  it  is  found  advantageous  to  proportion  the  amount 
of  metal  in  the  moving  parts  to  this  ratio.  For  "  A  "  run  No.  6, 
the  maximum  pressure  was  298  Ibs.,  and  the  mean  effective 
pressure  as  given  in  item  36  was  66.3  Ibs.,  thus  giving  a  ratio  of 
4.50.  For  "  B  "  run  No.  6,  the  maximum  pressure  was  238  Ibs., 
and  the  mean  effective  pressure  56.5  Ibs.,  giving  the  ratio  of  4.21. 

44.  Maximum  Pressure  to  Compression  Pressure. 

72.  Not  only  will  variations  in  this  relation  tend  to  show  changes 
in  the  quality  of  the  mixture,  due  either  to  fluctuations  in  the 
quality  of  gas  used,  or  to  differences  in  the  proportions  of  air  to 
gas;  but  it  also  gives  insight  into  possible  changes  in  the  form 


46  WOBKING  DETAILS  OF  A  GAS  ENGINE  TEST. 

of  the  combustion  chamber  for  securing  the  best  possible  flame 
propagation  after  explosion,  thus  insuring  the  most  complete  com- 
bustion of  the  mixture,  or  maximum  measure  of  heat  that  becomes 
effective. 

It  has  been  jclaimed  that  conditions  have  been  attained  under 
which  this  ratio  has  reached  a  figure  as  high  as  ten,  but  in  general 
it  is  found  to  be  about  three  or  three  and  one-half,  and  occasionally 
as  high  as  five.  Cases  have  been  reported  of  six  and  seven,  but 
investigation  revealed  the  fact  that  the  pressures  were  measured 
from  the  atmospheric  line.  "  A  "  run  No.  f  =  3.28.  "  B  "  run 
No.  6  =  2.62. 


45.    Value  of  R. 

73.  In  order  to  compute  the  temperatures  corresponding  to  dif- 
ferent points  in  the  indicated  diagram,  it  is  necessary  that  the 
temperature  of  some  one  point  be  known,  and  it  is  for  this 
reason  that  the  temperature  of  the  exhaust  gases  proves  of  so 
much  interest. 

In  engines  of  the  ordinary  size  it  is  hardly  possible  to  perceive 
by  means  of  the  indicator  diagram  when  a  high-pressure  spring  is 
used  any  considerable  reduction  in  the  pressure  of  the  mixture 
just  after  entering  the  cylinder.  In  most  cases  the  reduction  in 
pressure  is  slight  and  has  very  little  effect  upon  the  temperatures, 
and  it  is  sufficiently  accurate  to  regard  the  pressure  of  the  mixture 
at  full  cylinder  volume  as  that  of  the  atmosphere,  or  14.7  pounds 
per  square  inch.  If  the  temperature  of  a  perfect  gas  varies  during 
expansion,  the  product  of  the  pressure  and  volume  is  in  proportion 
to  the  absolute  temperature. 

"  R  "  is  the  constant  which  enters  into  the  mathematical  state- 
ment of  the  above  law,  viz.;  PV  —  ET. 


Data  Given. 
=  atmospheric  pressure  per  sq.  ft. 


=  2,117  Ibs.  per  sq.  ft.  p  ^   _ 

0a  =  total  vol.  of  cylinder  in  cu.  ft. 
Tm  =  absolute  temperature  of  mixture 
filling  cylinder  before  compres- 
sion begins. 
=  item  29  +  459°. 

To  Find— 
R  —  a  constant. 


Solution. 


By  the  above  law  : 


WOBKING  DETAILS   OF   A  GAS  ENGINE  TEST. 


47 


Examples. 
A"  Run  No.  6: 

Po  =  2,117  Ibs.  per  sq.  ft. 

t>a  =  -260  CU.  ft. 

Tm  =  106°  +  459°  =  565°. 

B  "  Run  No.  6  : 

Po  =  2, 117  Ibs.  persq.  ft. 
0a  =  .1844cu.  ft. 
^,  =  113°  +459°  =  572°. 


5<2 


46.   Temperature^  Degrees  Fahr.,  at  Compression. 

74.  Having  determined  "R"  as  in  45,  the  temperatures  cor- 
responding to  any  point  in  the  diagram  are  readily  determined 
by  the  general  formula  used  in  obtaining  "R"  after  solving  for  T. 


Data  Given. 
In  general. 

P  =  pressure  in  Ibs.  per  sq.  ft. 
V=  corresponding  vol.  in  cu.  ft. 
R  =  constant  determined  in  45. 

To  Find— 

T  =  absolute  temperature  corresponding 
to  the  point  of  the  diagram  se- 
lected. 

For  the  temperatures  of  compression. 

Examples. 

"A"  Run  No.  6: 
P  —  pressure  at  compression  per  sq.  ft. 

=  91  x  144  =  item  35  x  144. 
V  —  Vb  =  clearance  vol.  —  .Ooo  cu.  ft. 
R  =  .973  from  45. 

"B"  Run  No.  6. 
P  —  pressure  at  compression  per  sq.  ft. 

=  91  x  144  —  item  35  x  144. 
V  =  vb  =  clearance  vol.  =  .037. 
R  =  .681  from  45. 


rp  


Solution. 
PV 


R 


T  -  459°  =  F° 


T  = 


91  x  144  x  .055  __ 


7410  _  4590  _  2 


Tb  =       >LJ<_-        -  7110 
711° -459°  =252°F. 


47.  Maximum  Temperature,  Degrees  Falir. 

75.  Since  the  maximum  temperature  does  not  necessarily  cor- 
respond to  the  maximum  pressure,  but  depends  upon  the  maxi- 
mum value  of  the  product  of  pressure  -and  volume,  it  would  in 
general  be  determined  by  the  formula  used  in  46. 

In  cases  where  the  ignition  line  rises  vertically  from  the  point 


48 


WOBKING  DETAILS  OF  A  GAS   ENGINE  TEST. 


of  maximum  compression  and  where  the  expansion  curve  drops 
at  once  from  the  maximum  pressure,  it  is  apparent  that  the  maxi- 
mum temperature  corresponds  to  the  maximum  pressure.  Under 
these  conditions,  the  volumes  being  equal,  the  absolute  tempera- 


Fernald 


FIG.  19 


tures  will  be  proportional  to  the  pressures.  The  diagrams  from 
the  two  engines  considered  present  the  different  conditions  very 
clearly  in  the  runs  selected. 

Consider  first  the  diagram  for  run  No.  6,  test  "  A." 


Data  Given. 
pc  —  maximum   pressure,    Ibs.    per   sq. 

in.  =  item  36. 
pb  =  compression  pressure,  Ibs.  per  sq. 

in.  =  item  8%.*X 
Tb  =  absolute     temp,     at     compression 

=  item  46  +  459°. 

To  Find— 
Tc  =  absolute  maximum  temperature. 

Example. 

pc  =  298  Ibs.  per  sq.  in. 
pb  •=.  91  Ibs.  per  sq.  in. 
Tb  =  282°  +  459°  =  741°. 

If  the  same  computation  be  made  by 
the  formula  of  46,  the  clearance  volume 
vb,  is  necessary. 

c6  =  .055  cu.  ft. 


Solution. 


Tc  =  741  ~  =  2.429° 
2,429°  -  459°  =  1,970°  F. 

By  the  method  of  46 

g,=898xmx.0»5  = 

.y  t  o 
2,429°  -  459°  =  1,970°  F. 


Consider  the  diagram,  Fig.  20,  for  run  No.  6  of  test  "  B." 
'76.  In  this  case  it  is  not  apparent  without  some  calculation  at 

P  V 

which  point  the  maximum  temperature  will  occur.  Since   T  =     ^ 

it  is  only  necessary  to  determine  the  point  for  which  the  product 


WOKKING  DETAILS   OF  A  GAS  ENGINE  TEST.  49 

of  the  pressure  and  volume  is  a  maximum.  The  most  direct  and 
simplest  method  seems  to  be  by  direct  trial  by  measurement,  as 
follows : 


Fernald 


Female! 


FIG.  20. 


For  the  points  0,  1,  2,  3,  4,  the  volumes  in  cubic  feet  are  re- 
spectively 

.0395    .      .0417  .0438  .0453  .0460 

and  the  pressures  in  pounds  per  square  inches  are 

238  233  228  225  221 

The  products  of  the  corresponding  pressures  and  volumes  are 

9.42  9.74  10.00  10.20  10.15 

showing  the  point  marked  3  to  have  the  highest  temperature. 
Using  the  value  of  R  deduced  in  45,  the  temperature  for  the  point 
3  is  found  to  be 


225  x  144  x  .0453 


=  1,700°  F. 


ENERGIES. 

48.  Brake  Work,  in  Foot  Pounds. 

77.  The  usual  method  of  measuring  the  output  of  an  engine  is 
by  means  of  some  form  of  friction  brake.  At  times  special  dyna- 
mometers are  used,  but  usually  some  form  of  the  simple  prony 
brake. 

For  moderate  powers  the  form  of  brake  shown  in  Fig.  21  has 
been  found  very  satisfactory. 

It  consists  of  two  or  more  cotton  or  hemp  ropes  one-half  or  five- 
eighths  inch  in  diameter  encircling  the  wheel  and.  held  in  place 
by  five  or  six  blocks  of  wood  fitting  loosely  over  the  rim  of  the 
wheel,  and  to  which  the  ropes  are  fastened.  The  bottom  tie-bar 
4 


50 


WORKING  DETAILS   OF  A   GAS   ENGINE  TEST. 


of  the  standards  is  fitted  with  a  knife  edge  which  rests  on  ordinary 
platform  scales.  The  upper  ends  of  the  ropes  are  attached  to  a 
movable  block,  which  can  be  adjusted  by  means  of  the  hand- 
wheels  to  produce  any  desired  friction  upon  the  wheel. 


FIG.  21. 


78.  The  downward  pull  of  the  ropes  produced  by  this  friction 
is  transmitted  through  the  frame  of  the  brake  to  the  scales. 

If  the  wheel  face  be  fairly  wide  and  the  diameter  of  the  wheel 
large,  the  surface  exposed  to  the  air  will  allow  sufficient  radiation 
to  keep  the  temperature  of  the  wheel  low  enough  to  avoid  the  neces- 
sity of  the  use  of  water.  This  form  of  brake  has  been  found  very 
steady,  requiring  little  regulation. 

While  the  writer  was  at  the  Case  School  of  Applied  Science, 
such  a  brake  was  used  upon  the  ten-foot  fly-wheel  of  a  Corliss  en- 
gine from  which  seventy-five  horse-power  was  readily  taken,  and 
no  water  was  found  necessary  for  a  continuous  run  of  three  hours. 
Six  ropes  one-half  inch  in  diameter  were  used,  the  wheel  rim  being 
fifteen  inches  in  width.  The  same  ropes  were  used  for  several 
seasons,  and  showed  no  signs  of  wear  or  burning.  In  many 
cases  other  forms  of  brake  would  undoubtedly  prove  more  con- 
venient or  desirable. 


WORKING  DETAILS  OF  A  GAS  ENGINE  TEST. 


51 


The  determination  of  the  brake  work  in  foot  pounds  is  as  fol- 
lows : 


Data  Given. 

P  —  net  pressure  on  scales,  in  Ibs. 
I  =  effective  lever  arm,  in  ft. 
JV  =  No.  revs,  per  time  interval. 

To  Find— 
Foot  pounds  per  time  interval. 

Examples. 
"A"  Run  No.  6  : 
P  =  70  Ibs. 
21  =  D  =  3.75  ft. 
N  =  2,679  revs,  for  10  mins, 
Tt  =  3.14. 

"B"  Run  No.  6: 
P  =  30  Ibs. 
21  =  D  =  3.25  ft. 
N  =  3,012  revs,  for  10  mins. 
it  =3.14. 


Solution. 

Ft   Ibs.  per  min.  =  P  •  2nl  •  (R.  P.  M.) 
In  case  of  the  special  rope  brake,  I  z 
radius  of  wheel,  or  21  =  1),  then 
ft.  Ibs.  per  int.  =  PnDN. 


Ft.  Ibs.  per  int.  = 

70  x  3.14  x  3.75  x  2,679 
=  2,210.000  ft.  Ibs.     • 


Ft.  Ibs.  per  int.  = 

30  x  3.14  x  3.25  x  3,012 
=  921,000  ft.  Ibs. 


49.  Brake  Work,  Foot  Pounds  per  Hour. 

79.  This  is  readily  deduced  from  the  last  deduction: 

For  "  A  "  Run  No.  6  =  2,210,000  x  6  =  13,260,000  ft.  Ibs. 
For  "  B  "  Run  No.  6  =     921,000  x  6  =    5,526,000  ft.  Ibs. 

50.  Brake  Horse-power,  B.  H.  P. 

80.  Horse-power  being 

ft.  Ibs.  per  min.          -D   TT  p  __  ft.  Ibs.  per  int.  from  48 

33,000        '  33,000  x  int. 

For  «  A  »  Run  No.  6  :  B.  H.  P.  =  £?^™     =  6.7. 

oo,OUO  x  10 

For  «  B  "  Run  No.  6  :  B.  H.  P.  =  -^J4'— °-  =  2.79. 


51.  British  Thermal  Units  Equivalent  to  B.  H.  P. 

81.  The  heat  unit  being  taken  as  the  consumption  standard,  it 
is  necessary,  in  order  to  determine  thermal  efficiencies,  to  express 


52 


WORKING   DETAILS   OF  A  GAS   ENGINE   TEST. 


the  horse-powers,  or  ratio  of  doing  work,  in  terms  of  this  unit. 
Since  one  thermal  unit  is  equivalent  to  778  foot  pounds,  to  convert 
horse-power  to  thermal  units  proceed  as  follows : 


Data  Given. 
1  H.  P.  =  33,000.  ft.  Ibs.  per  rain.    ,      B-  T- 
1  B.  T.  U.  =  778  ft.  Ibs. 


B.  H.  P.  =  brake  horse-power  of  50. 
int.  =  time  interval  of  item  2. 

To  Find— 
B.  T.  U.  per  int.  equivalent  to  B.  H.  P. 

Examples. 
"A  "  Run  No.  6  : 

B.  H.  P.  =6.70 

int.  =  10  mins. 

"B"  Run  No.  6: 

B.  II.  P.  =  2.79. 

int.  —  10  mins. 


Solution. 
min.  for 


B.  T.  U.  per 

int.  =  42.4  x  B.  H.  P  x  int. 


B.  T.  U.  per 

int.  =  42,4  x  6.70  x  10  =  2,840. 

B.  T.  U.  per 
int.  =42.4  x  2.79  x  10  =  1,180. 


52.  Indicated  Horse-power,  I.  II.  P. 

82.  The  indicated  horse-power  is  determined  by  means  of  the 
mean  effective  pressure  obtained  from  the  indicator  diagram. 
When  the  load  is  variable  these  diagrams  should  be  taken  at  fre- 
quent intervals,  and  it  is  often  advisable  to  allow  the  pencil 
to  trace  three  or  four  diagrams  on  the  same  card  and  use  the  aver- 
age mean  effective  pressure  obtained  from  these.  Under  uniform 
conditions  these  successive  tracings  will  show  little  variation. 
When  the  test  is  continued  for  many  hours,  so  that  the  time  inter- 
vals Are  long,  it  is  well  to  take  cards  at  stated  periods  during  the 
regular  interval.  These  periods  should  seldom  exceed  fifteen 
minutes.  When  the  regular  time  interval  for  all  readings  is  ten 
or  fifteen  minutes  one  card  for  each  interval  is  sufficient,  provided 
slight  variations  only  are  found  in  the  different  cards  as  taken 
(see  remarks  under  Pressures  for  Indicator  Cards,  following  para- 
graph 31  of  this  paper,  and  for  the  calibration  of  indicator  springs, 
see  section  xiv.  of  paper  No.  0943,  the  "  Report  of  the  Committee 
of  this  Society  for  Standardizing  a  System  of  Testing  Steam 
Engines." 


WORKING  DETAILS   OF  A   GAS  ENGINE  TEST. 


53 


TO    DETERMINE    THE    INDICATED    HORSE-POWEK. 


P  =  M.  E.  P.  from  diagram  =  item  36. 
L  =  length  of  strokes  in  ft. 
A  =.  area  piston  in  sq.  ins. 
-N  =  No.  explosions  per  min. 

Examples. 
"A"  Run  No.  6: 

P  =  66.3  Ibs. 
L  =  1.04  ft. 
A  =  28.3  sq.  ins. 
N=  133.9. 

"B"  Run  No.  6: 

P  -  56. 5  Ibs. 
L  =  .75ft. 
A  =28.3  sq.  ins. 
.#  =  93.4. 


~  33,000 


66.3  x  1.04  x  283 
33,000 


33,000 


133.9 


=  7.93 


53.  British  Thermal  Units  Equivalent  to  /.  77.  P. 

83.  The  determination  is  the  same  as  that  of  51,  with  the  ex- 
ception that  indicated  horse-power  is  substitued  for  brake  horse- 
power. 


A"  Run  No.  6  :     I.  H.  P.  _=  7.93 
B"  Run  No.  6  :     I.  H.  P.  =  3.40 


B.  T.  U.  =  42.4  x  7.93  x  10  =  3,360 
B.  T.  U.  =  42.4  x  3.4    x  10  -  1,440 


54.  Gas  Horse-power.    55.  B.  T.  U.  Equivalent  to  Gas  II.  P.  —  H^. 

84.  In  order  to  determine  the  theoretically  possible  power,  it  is 
necessary  to  know  the  heat  equivalent  of  the  fuel  used.  This  heat 
of  combustion  may  be  determined  by  chemical  analysis  or  by 
means  of  a  calorimeter.  The  calorimeter  generally  recommended 
seems  to  be  the  Mahler,  for  solid  fuels  and  oils,  and  Junker  for 
gas.  (See  "  Report  of  Committee  on  Standardizing  a  System 
of  Testing  Steain  Engines/7  paper  ~No.  0943,  and  "  Efficiency  Test 
of  a  One  Hundred  and  Twenty-five  Horse-power  Gas  Engine/'  by 
C.  H.  Robertson,  paper  No.  907,  American  Society  of  Mechanical 
Engineers.) 

Since  the  mixtures  considered  are  explosive  mixtures  and  are  used 
under  such  conditions,  a  calorimeter  designed  and  calibrated  for  such 
conditions  should  be  used  for  accurate  determinations.  Such  a 
calorimeter  is  now  in  operation  at  Columbia.  When  it  is  inconven- 
ient to  secure  either  a  chemical  or  calorimeter  test,  it  is  usually 
possible  to  learn  through  the  company  supplying  the  fuel  its  ap- 
proximate heat  equivalent. 


54: 


WORKING  DETAILS  OF  A  GAS  ENGINE  TEST. 


The  number  of  heat  units  is  equal  to  the  heat  equivalent  of  one 
pound  of  coal  or  oil,  or  one  cubic  foot  of  gas,  multiplied  by  the 
quantity  of  fuel  in  corresponding  units. 


Data  Given. 

Hf  =  heat  of  combustion  of  fuel  deter- 
mined by  analysis  or  calorimeter. 
.F=lbs.   of  coal  or  oil,  or  cu.  ft.   of 
standard  gas  per  interval. 

To  Find- 
Hi  =  heat  equivalent  to  G.  H.  P. 

//,  x  778 


Gas  H.  P.  = 


33,000  x  int. 


Examples. 
"  A  "  Run  No.  6  : 
Hf  —  650  B.   T.   U.   per  cu.  ft.  gas  at 

standard  temp.  60°  F. 
F '  =  25.2  cu.  ft.  gas  for  10  mins. 

=  item  25  -T-  6. 
int.  — .  10  mins.  =  item  2. 

"B"  Run  No.  6  : 
///  =  650  B.   T.  U.   per  cu.  ft.  gas  at 

standard  temp.  60°  F. 
F  —  14.6  cu.  ft.  gas  for  10  mins. 

=  item  25  -f-  10. 
int.  =  10  mins.  —  item  2. 


Solution. 


=  Hf  x  F 


//,  =  050  x  25.2  =  16,400  B.  T.  U. 

16.400  x  778 
<*»»•*'=  33.000x10   =88-6- 


77,  =  6oO  x  14.6  =  9,500  B.  T.  U. 

GasH  P  -  9'500  x  778  -  2*  4 
MM'-r-  -33,000  x  10  ~ 


56.  Heat  Supplied,  B.  T.  U.,from  Indicator  Card  =  ///. 

85.  There  is  always  a  wide  discrepancy  between  the  supply  of 
heat  shown  by  the  indicator — by  the  pressure  rise  line  BC  of  the 
diagrams — and  that  shown  by  the  calorimeter  or  chemical  test  of 
the  fuel. 

The  great  difference  in  the  values  of  these  two  quantities  is 
readily  seen  by  a  glance  at  items  66  and  67,  which  show  the 
efficiencies  based  on  these  different  values. 

The  computation  for  the  heat  supplied,  as  shown  by  the  indica- 
tor diagram,  involves  not  only  the  temperature  of  compression 
and  the  corresponding  temperature  from  the  expansion  curve,  but 
strictly  the  specific  heat  of  the  gases  before  and  after  explosion, 
and  during  the  process  of  explosion — a  value  which  is  indeter- 
minate— and  the  total  weight  of  these  gases.  This  tends  to 
seriously  complicate  the  problem,  but  the  specific  heat  will  be  as- 
sumed the  same  before  and  after  explosion  and  can  in  both  cases 
be  regarded,  without  serious  error,  as  the  value  given  for  air. 


WORKING   DETAILS   OF   A   GAS   ENGINE   TEST. 


55 


Gicen.  Solution, 

Tm  =  absolute  temperature  of  mixture  \ 
in  cylinder  before  compression 
=  item  29  +  459°. 

Tag  =  absolute  temp,  of  entering  air 
and  gas  as  computed  in  para- 
graph 29. 

Vag  =  vol.  of  entering  air  and  gas  per 
explosion  at  Tag  as  computed 
in  Part  I.  of  29. 

rb  —  clearance  vol.  of  cylinder. 

w$  =  wgt.    per  cu.   ft.  of  mixture  at 

Tm  as  computed  in  30.  Tm 

Cv  =  specific  heat  at  constant  vol   — 

.1691.  vt  = 

T,  =  absolute   temp,    of   point    C  of  !        wm  — 
diagram. 

TI,  =  absolute  temp,  of   compression 

=  item  46  4-  459°. 

Kxps  =  total    explosions   per  time  in- 
terval. 

To  Find— 

vt  •=  vol.  entering  air  and  gas  at  Tm.  \ 
vt  =  total  vol.  per  explosion  of  mix-  j 

ture  before  compressing. 
wm  =  total  wgt.  of  mixture  in  cylinder.  , 
H\   =  heat  supplied   in   B.  T.  U.  peri 
time  interval. 

Examples. 
"A"  Run  No.  6  : 

Tm  =  106°  +  459°  =  565°. 
Tag  =  545°. 

Vag=    -1646    CU.    ft. 

f>6  =  .055  cu.  ft. 
w,  =  .0701  Ib. 
C,=  .1691. 

T  =  1,970°  +  459°  =  2,429°. 
Tb  =  282°  +  459°  =  741°. 
Exps.  =  1,339  for  10  mins. 

86.  The  determination  of  the  temperature  (Tc),  corresponding 
to  the  point  C  of  the  diagrams  is  not  always  as  readily  made  as 
in  the  case  just  cited,  as  may  be  observed  by  inspecting  Figs.  10 
and  20.  In  Fig.  19,  which  corresponds  to  run  No.  6,  of  test 
"  A,"  the  line  BC  of  the  diagram  coincides  with  the  line  drawn 
through  B  parallel  to  the  line  of  zero  volumes,  thus  making  Tc 
and  the  maximum  temperature,  deduced  in  47,  identical.  When 
these  fortunate  conditions  do  not  exist,  as  in  Fig.  20,  or  run  ]STo. 


«e=  .1646?^=  .I7l0cu.  ft. 
545 

v.  =  .171  +  .055=  .226cu.  ft. 
wm  =  .  226  x  .0701  =  .158  Ib. 
Hi  =  .1691  (2,429  -  741)  .158  x  1,839 
=  6,040  B.  T.  LT. 


56  WORKING  DETAILS   OF  A   GAS  ENGINE   TEST. 

6  of  test  "B,"  it  is  necessary  to  continue  the  expansion  curve  to  the 
point  C,  as  in  the  computation  for  II'  \  it  is  specified  that  the  tem- 
peratures must  be  taken  for  constant  volume  points. 

When  any  question  exists  regarding  the  true  value  of  n  for  the 
equation  of  the  expansion  curve  near  the  point  (7,  the  curve  may 
be  continued  from  points  below  by  the  eye  and  the  value  thus  ob- 
tained for  C  checked  with  that  found  by  the  equation.  In  the 
present  instance  the  pressure  at  C  was  found  to  be  about  282 
pounds. 

Having  determined  the  pressure  at   C  as  just  indicated,   the 

PV 

temperature  maybe  readily  computed  by  the  formula  T-    —p- 

or  more  easily  by  direct  proportion,  since  the  temperature  at  B 
is  already  known.  By  the  latter  method 

Tr=Tbl±  or  Tc  =  711  \  f  =  2,203°  or  1,744°  F. 

7?6 

This  result  is  quickly  checked  by  the  other  method,  or 
288  x  144  x  .037 


Continuing  with  the  original  problem, 


B"  Run  No.  6  : 

Tm  =  113°  H-  450°  =  572° 


vb  =  .037  cu.  ft.  vs  =  .0976  +  .037  =  .1346  cu.  ft, 

•tO>  =  .0692  Ib.  :    wm  =  .1346  x  .0692  =  .009:3  lb. 

C,.  =  .1691  ///  =  .1691  (2,203  -  711)  .0093  x  934 

Tc  =  2,203°  =2,190  B.  T.  U, 
Tb  =  711° 
.Ztapa.  =--  934  per  10  min. 

87.  In  the  solution  of  Heat  Extracted,  B.  T.  U.  from  indicator 
cards,  =  HJ,  item  58,  the  same  values  of  Cv,  wm,  and  Exps.  enter 
the  calculations.  It  is,  therefore,  well  in  working  the  above  to  take 
the  product  Cv,  wm,  Exps.  for  each  run  and  tabulate  the  results 
under  a  heading  "  K  ??  for  further  use. 

Thus  for  "A"  No.  6,  K=  .1691  x  .158  x  .1339  -  3.58, 
and  for  "B"  No.  6,  K=  .1691  x  .0093  x  934  =  1.47. 


WOBKING  DETAILS   OF  A  GAS  ENGINE  TEST. 


57 


57.  Heat  Extracted,  B.  T.  U.,  ~by  Observation  =  7/2. 

88.  This  value  is  determined  by  an  analysis  of  the  exhaust  gases 
from  which  the  heat  equivalent  of  a  cubic  foot  of  these  gases  is 
determined. 


Data  Given. 

Te  =  absolute   temp,    exhaust    at   at- 
mospheric pressure. 
=  item  14  of  log  +  459°. 
Tm  —  absolute  temp,  of  entering  mix- 
ture =  item  29  +  459°. 
Op  =  specific  heat  at  constant  pressure. 
Tag  =  absolute  temp,  of  combined  air 

and  gas  as  found  in  29. 
vag  =  combined  vol.  of  air  and  gas  per 

explosion  at  Tng. 
Tk  =  absolute    temp,    of    exhaust   as 

analyzed. 

h  =  B.  T.  U.  per  cu.  ft.  exhaust 
gases  at  Tk  as  found  by 
analysis. 

Exps.  =  explosions  per  time  interval. 
w^  ~-  weight  per  cu.  ft.  by  analysis. 

To  Find— 

vk  =  vol.  in  cu.  ft.  at  Tk  per  explosion. 
w/c  —  total  weight  per  explosion. 
Hz  =  total  heat  exhausted,  B.  T.  U.,  per 
time  interval. 


Solution. 


Tk 

®ag  T 
-L  aa 


2  =  Cp  (Te  - 


wk  x  Exps.  +  h 


58.  Heat  Extracted,  B.  T.  U.,  from  Indicator  Card  =  H2'. 

89.   This  is  the  heat  thrown  off  in  the  exhaust  as  derived  from 
the  pressures  shown  by  the  indicator  card. 


Data  Given. 
Th  =  absolute  temp,  of  exhaust  =•  item 

37  +  459°. 

Tm  =  absolute  temp,  of  mixture  at  at- 
mospheric pressure  =  item  29  + 
459°. 
K  =  Cv  x  wm  x  Exps.  as  found  in  57. 

To  Find- 

Hv   =heat   rejected,  B.T.U.,  per   time 
interval. 


Solution. 


h-  Tm} 


58 


WOBKING  DETAILS  OF  A  GAS   ENGINE  TEST. 


Examples. 
"A"  Run  No.  6  : 
Th  =  1,387°  +  459°  =  1,846°. 
Tm  =  106°  +  459°  =  565°. 
K  =  3.58  from  57. 

"  B  "  Run  No.  6  : 
Th  =  1,120°  +  459°  =  1,579°. 
Tm  =  113°  +  459°  =  572°. 
K=IA1  from  57. 


=  3.58  (1,846-565)  =  4,580  B.  T.  U. 


=  1.47  (1,579-572)  =  3,480  B.  T.  U. 


Both  in  this  solution,  and  in  that  of  57,  since  the  difference  of 
temperatures  is  involved,  the  common  factor  may  be  omitted  if 
desired,  and  the  temperatures  taken  directly  from  the  report  blank 
in  Fahrenheit  degrees.  Thus  for  "  A  "  run  No.  6. 


th  =  1,120' 
tm  =  113°. 


1.47  (1,120-113)  =  1,480  B.T.U. 


59.  Indicated  Horse-power  Minus  Brake  Horse-power. 

90.  The  difference  between  these  powers  is  frequently  called 
the  friction  horse-power.     It  is  not  alone  the  power  required  of 
the  engine  to  drive  its  own  mechanism,  but  includes  the  error  due 
to  inability  to  take  indicator  cards  every  explosion.     This  is  es- 
pecially important  with  two  cycle  engines  with  throttling  gover- 
nors. 

The  calculation  consists  simply  in  subtracting  the  value  of  item 
50  from  item  52. 

For  "  A  "  run  No.  6  this  is  7.93  -  6.70  =  1.23, 
and  for  "B"  run  No.  6,  3.40  -  2.79  =  0.61. 

60.  Throttling  of  the  Entering  Mixture,  Cu.  Ft.  per  Explosion. 

91.  It  is  found,  as  might  be  expected,  that  the  final  volume  of 
the  mixture  in  the  cylinder  before  compression  is  not  equal  to  the 
full  cylinder  volume  if  the  mixture  is  taken  at  atmospheric  pres- 
sure.   This  is  caused  in  part  by  the  brief  time  allowed  for  entering, 
and  in  part  by  valve  friction.    In  large  engines  this  throttling  may 
become  serious,  and  all  valves  should  be  positively  moved  and  not 
moved  by  suction. 

Owing  to  many  conditions  that  affect  this  result,  the  calculation 
of  the  amount  is  approximate  only,  but  gives  an  idea  of  results  of 
this  throttling  action. 


WuBKING  DETAILS  OF  A  GAS  ENGINE  TEST. 


59 


In  computing  56  the  value  vg  obtained  is  equal  to  the  total  vol- 
ume for  explosion  of  mixture  at  atmospheric  pressure  before  com- 
pression, expressed  in  cubic  feet.    The  total  volume  of  the  cylinder 
minus  this  value  gives  the  effect  of  throttling. 
"  A  "  Run  No.  6. 

Total  cylinder  vol.  =  .260  cu.  ft. 

From  57,  v8  =  .226  cu.  ft. 

Throttling       .034  cu.  ft. 

"  B  "  Eun  No.  6. 

Total  cylinder  vol.  =  .1844  cu.  ft. 

From  57,  v8  —  ,1346  cu.  ft. 

Throttling  =  .0498  cu.  ft. 

61.  Percentage  of  Throttling. 

This  is  the  ratio  of  the  cubic  feet  throttled  to  the  total  cylinder 
volume  in  cubic  feet. 

"  A  "  Run  No.  6  : 

"  B  "  Run  No.  6  : 


034 
~    =  13.1  per  cent. 


=  27.0  per  cent. 


62.    Work  that  would  he  Added  if  Expansion  were  Complete. 

92.  A  point  of  considerable  interest  was  presented  in  attempting 
to  make  the  computations  involved  in  this  column.  The  math- 
ematical work  required  is  given  below  : 


FIG.  22. 
To  find  the  area  under  the  expansion  curve  proceed  as  follows 


The  general  expression  for  the  area  is 

ffla 

A-\     pdv, 
M 


60  WORKING  DETAILS   OF  A  GAS  ENGINE  TEST. 

Substituting  the  value  of  p  found  above 

f«2 

A  —  pi  Vin       v~ndv 


which  reduces  to 

A  _ 

.z-L    — 


_ 

. 

n  —  1 


A  glance  at  this  formula  reveals  the  fact  that  the  value  of  A, 
which  corresponds  to  the  work  done,  depends  upon  the  value  of  n, 
and  in  carrying  out  the  solution  any  variation  in  n  makes  such 
serious  variation  in  the  value  of  A  that  no  dependence  can  be  placed 
upon  the  values  obtained  unless  the  values  of  n  can  be  guaranteed 
correct.  The  time  at  command  does  not  allow  further  investiga- 
tion at  present,  but  the  trial  solutions  revealed  a  possible  method 
of  making  more  accurate  determinations  of  the  value  of  n  than 
can  possibly  be  made  by  the  method  employed  in  paragraph  28. 
The  difficulty  arising  from  slight  variations  in  n  prevented  any  at- 
tempt to  supply  the  results  called  for  in  this  column  of  the  report. 

EFFICIENCIES. 

93.  The  efficiency  may  be  expressed  in  many  different  .forms, 
as  indicated,  and  in  general  it  is  very  essential,  when  referring  to 
the  efficiency  of  a  gas  engine,  to  designate  clearly  to  which  effi- 
ciency reference  is  made,  in  order  to   avoid  serious  misunder- 
standing. 

The  mathematical  deductions  are  so  fully  indicated  in  the  head- 
ings of  the  various  columns  that  further  explanation  about  the 
details  seems  unnecessary,  and  only  general  remarks  will  be  made 
under  each  paragraph. 

£o     T/    -L      -7  item  50 

63.  Mechamcal  -    -- 

^tem  52 

94.  This  efficiency  is  the  ratio  of  the  power  which  can  be  taken 
from  the  engine  to  the  power  shown  by  the  indicator  card.     It 
therefore  depends  much  upon  the  smooth,  easy  running  of  the  en- 
gine itself. 


WORKING  DETAILS   OF  A  GAS  ENGINE   TEST.  61 

"  A  "  Run  No.  6  =  ^  =  .846 

i  .UO 

9,  7Q 

"  B  "  Eun  No.  6  =  |^  =  .822 

64  and  66.   Thermal  for  B.  II.  P.  and  /.  //.  P. 

95.  In  these  cases  the  efficiency  is  based  upon  the  total  heat  put 
into  the  engine  as  shown  by  the  calorimeter  or  chemical  analysis 
of  the  fuel.  Item  64  shows  what  percentage  of  the  total  heat 
in  the  fuel  is  converted  into  useful  work  and  item  66  shows 
the  percentage  of  the  total  heat  converted  for  both  useful  and  use- 
less work. 

"A"  Run  No.  6: 


B"  Run  No.  6: 


65  and  67. 

If  the  basis  for  computing  the  efficiency  be  that  of  the 
heat  actually  shown  to  be  supplied  by  the  indicator,  then  the 
thermal  efficiency  is  much  higher.  This  basis  has  been  used  in 
computing  items  65  and  67. 

"A"  Run  No.  6: 


B"  Run  No.  6: 

F°"-H.P.=S 


68,  69  and  70. 

96.  In  these  columns  are  given  other  methods  of  estimating  the 
efficiency,  based  as  before  on  both  the  heat  supplied  and  extracted 


62  WOKKING   DETAILS  OF  A   GAS   ENGINE   TEST. 

as  determined  directly  from  the  gases,  and  as  determined  from 
the  indicator  diagram. 

TT  l    _       TT  I 

For  item  69,  — l— — — i  ,  the  efficiencies  were 
Hl 

6,040  -  4,580 
"A"RunNo.6:        -^-     =  .242 

"B"  Run  No.  6:    8'1W  ~J!'g°  =  .824 

iC,  lyu 

The  necessity  of  clearly  designating  the  efficiency  selected  is 
made  very  apparent  by  a  comparison  of  the  values  given  in  the  pre- 
ceding paragraph. 

STANDARD    GAS    PER    HOUR. 

97.  In  order  for  comparison  to  be  made  it  is  very  essential  that 
some  standard  be  adopted  for  estimating  the  quantity  of  gas  used. 
The    basis    of   reckoning   item    25,    which    has   previously   been 
recommended  by  a  few  writers,  seems  to  be  the  proper  one,  and 
therefore  standard  gas  is  interpreted  to  mean  gas  under  atmos- 
pheric pressure  and  at  a  temperature  of  60  degrees  Fahr. 

71.  Fuel  for  Indicated  Horse-power  per  Hour. 

98.  This  is  readily  obtained  by  dividing  the  values  in  column 
25  by  the  corresponding  values  in  column  52. 

"  A  "  Run  No.  6  :     ^^  =  19  cu   ft-  Per  hr- 

<  .  "o 
"  B  "  Run  No.  6  :     ^^  =  25.7  cu.  ft.  per  hr. 

72.  Fuel  and  Igniter  for  Indicated  Horse-power. 

In  case  of  flame  or  hot  tube  ignition  the  gas  used  should  be 
passed  through  a  separate  meter  and  for  the  data  in  this  column 
the  quantity  of  standard  gas  used  for  fuel  combined  with  that 
used  for  the  igniter  will  give  the  total  standard  gas  per  hour.  This 
quantity,  divided  by  the  indicated  horse-power,  will  give  the  de- 
sired value. 

73  and  74.  Fuel,  and  Fuel  and  Igniter,  per  Brake  Horse-power. 

99.  The  method  of  procedure  is  the  same  as  in  71  and  72,  save 
that  the  brake  horse-power  is  now  used  instead  of  the  indicated 
horse-power. 


WORKING    DETAILS   OF  A   GAS   ENGINE   TEST.  63 

FUEL    PETC   B.   H.  P. 

il  A"  Run  No.  6  :    ^~  =  22.5  cu.  ft. 
"  B  "  Run  No.  6  :    |-^  =31.4  cu.  ft. 

75.   Cost  per  Indicated  Horse-power  per  Hour,  Cents. 

100.  The  value  $1.00  per  thousand  cubic  feet  of  standard  gas  is 
taken  as  a  basis  for  determining  the  comparative  cost  of  different 
engines.   A  similar  deduction  would  be  made  for  other  fuels,  based 
on  an  average  cost  of  that  fuel.     In  case  the  gas  used  for  the 
igniter  is  reckoned  in  this  cost,  then  when  electric  ignition  is  used 
the  cost  of  maintaining  the  battery  should  also  be  considered,  in 
order  to  make  a  proper  comparison.    For  relative  cost  it  is  as  well 
to  disregard  the  igniter  and  base  the  computation  alone  on  the 
quantity  of  fuel  alone. 

Since  the  fuel  used  in  run  No.  6  was  19  cubic  feet  for  "  A  "  and 
25.7  cubic  feet  for  "  B,"  it  is  readily  seen  that  the  cost  per  indi- 
cated horse-power  per  hour  was  1.9  cents  and  2.57  cents  re- 
spectively. 

TOTALS    AND    AVERAGES. 

101.  In  order  to  get  a  general  series  of  values  for  the  engine 
in  question  it  is  often  well  to  average  the  results  obtained  under 
the  same  conditions.     For  this  purpose  space  has  been  reserved 
on  the  report  blank  for  the  necessary  totals  and  averages. 

HEAT  BALANCE. 

102.  By  means  of  the  heat  balance  a  general  idea  is  formed  of 
the  distribution  and  uses  of  the  heat.     As  is  apparent,  the  first 
result  is  .the  average  of  the  results  in  item  53;  the  second  of  those 
in  item  12;  the  third  of  those  in  item  58.     To  the  last  result  is 
charged  all  the  heat  otherwise  unaccounted  for.     The  average  of 
the  British  thermal  units  obtained  from  the  gas  as  determined 
from  item  55  is  used  as  the  basis  in  determining  the  percentages. 


PART    II. 

A  METHOD    OF    DETERMINING    THE    TEMPERATURES    OF    EXHAUST 

GASES. 


A    METHOD 

OF 

DETERMINING   THE   TEMPERATURE 

OF 

EXHAUST    GASES. 


1.  IN  preparing  detailed  specifications  and  instructions  for  con- 
ducting tests  of  gas  engines  (paper  No.  0933  presented  before 
this  Society  at  this  meeting)  the  attention  of  the  writer  was  di- 
rected to  the  necessity  of  an  accurate  and  inexpensive  method  of 
determining  the  temperatures  of  exhaust  gases.     This  problem 
had  apparently  received  little  attention,  at  least  not  sufficient  to 
develop  any  simple  means  of  making  accurate  determinations.     In 
cases  in  which  the  results  seemed  to  be  reasonable,  the  apparatus 
used  was  far  too  expensive  or  too  delicate  for  ordinary  conditions, 
and  efforts  were  at  once  centred  upon  the  desired  solution. 

2.  In  the  books  at  hand  on  engine  tests,  no  mention  is  made 
of  any  method,  and  even  in  the  very  recent  report  of  the  com- 
mittee appointed  by  this  Society  "  To  Codify  and  Standardize  the 
Methods  of  Making  Engine  Tests,"  the  committee  says  (paragraph 
XX.)  :  "The  computation  of  temperatures  corresponding  to  various 
points  in  the  indicator  diagram  is,  at  best,  approximate.     It  is  pos- 
sible only  when  the  temperature  of  one  point  is  known  or  as- 
sumed, or  when  the  amount  of  air  entering  the  cylinder  along 
with  the  charge  of  gas  or  oil,  and  the  temperature  of  the  exhaust 
gases  are  determined.^      In   the   fine-print   detailed   instructions 
under  the  same  paragraph  the  report  states,  "  T'  may  be  taken 
as  the  temperature  of  the  exhaust  gases  leaving  the  engine,  pro- 
vided the  engine  is  not  of  the  i  scavenging '  type." 

Again,  in  referring  to  the  value  represented  by  T  in  formula 


68 


DETERMINING   THE   TEMPERATURE    OF   EXHAUST   GASES. 


B  of  the  same  paragraph  is  found  the  expression,  "If  T  be  the 
observed  temperature  of  the  exhaust  gases." 

3.  While  references  thus  made  indicate  the  necessity  of  obtain- 
ing these  temperatures,  yet  nowhere  in  the  report  is  there  any 
suggestion  of  a  method  of  making  these  determinations.  Even 
if  pyrometers  and  thermometers  are  regarded  as  sufficiently  ac- 
curate, yet  no  measurements  made  at  or  near  the  muffler  can  give 
the  true  temperature  of  the  exhaust  gases  unless  proper  correc- 
tions be  made  for  the  fluctuations  in  pressure.  This  at  first  ap- 
pears to  present  little  difficulty,  but  more  careful  thought  shows 
the  fallacy  of  the  first  impression. 

Consider  for  a  moment  the  action  taking  place  at  the  opening 


FIG.  1. 


of  the  exhaust.  Although  the  gases  in  the  cylinder  have  under- 
gone rapid  expansion  after  explosion,  yet  the  expansion  is  far  from 
complete,  and  at  the  point  of  release  the  pressure  is  still  relatively 
high,  as  shown  by  a  glance  at  Fig.  1. 

4.  At  the  instant  the  exhaust  opens  there  is  an  outrush  of  gases 
at  this  high  pressure  and  correspondingly  high  temperature.  Then 
follows,  upon  the  forward  stroke  of  the  engine,  a  flow  of  a  large 
mass  of  gases  through  the  exhaust  port,  at  a  pressure  little  above 
that  of  the  atmosphere  and  at  a  temperature  necessarily  less  than 
that  of  the  first  discharge.  In  order  to  make  the  succession  of 
events  more  apparent  an  indicator  was  attached  directly  to  the 
exhaust  pipe,  and  the  cards  obtained,  as  shown  in  Figs.  2  and  3, 
verified  the  statements  just  made  in  regard  to  the  action  taking 
place  within  the  pipe.  The  diagrams  represent  the  same  condi- 
tions, the  spring  used  for  Fig.  2  being  only  one-half  as  heavy  as 
that  used  in  Fig.  3. 


DETERMINING   THE    TEMPERATURE    OF   EXHAUST    GASES.  69 

5.  There  is,  as  it  were,  a  mixture  of  pressures  in  the  exhaust 
pipe  and  muffler,  and  also  a  corresponding  mixture  of  tempera- 


FIG.  2. 


tures,  which  must  rapidly  adjust  themselves  to  an  equilibrium  of 
pressures  and  of  temperatures. 

Temperatures  determined  at  the  muffler  are,  therefore,  not  the 
temperatures  corresponding  to  the  pressure  at  exhaust,  but  those 
corresponding  to  a  much  lower  pressure,  which  is  not  determined. 
This  accounts,  no  doubt,  for  the  very  low  values  of  exhaust  tem- 
peratures which  have  been  reported  even  by  recognized  authorities 
upon  gas-engine  problems. 

The  problem,  therefore,  resolves  itself  into  the  determination 
of  the  temperatures  of  the  exhaust  at  some  known  pressure. 

6.  As  a  matter  of  simplicity  atmospheric  pressure  was  the  natu- 


PIG.  3. 


ral  selection,  and  a  method  was  at  once  sought  for  reducing  the 
exhaust  gases  to  atmospheric  pressure  without  losing  any  of  the 
heat  to  which  they  are  entitled. 

It  was  at  once  decided  that  a  receiver,  of  a  form  to  be  deter- 
mined, should  be  placed  close  to  the  exhaust  outlet  of  the  engine, 
and  some  means  devised  for  admitting  the  exhaust  gases  and  al- 


70  DETERMINING    THE    TEMPERATURE    OF    EXHAUST    GASES. 

lowing  their  pressure  to  fall  to  that  of  the  atmosphere.     The  de- 
sired temperature  could  then  be  ascertained. 

7.  What  the  form  of  the  receiver  should  be  was  not  at  first 
apparent,  and,  as  practically  no  information  could  be  found  bear- 
ing upon  the  subject,  the  problem  was  reduced  to  one  of  experi- 
ment. 

The  first  steps  in  the  development  were  necessarily  very  crude 
and  the  results  were  of  value  only  as  furnishing  a  basis  upon 
which  to  judge  future  determinations,  and  as  such  were  of  great 
value. 

The  first  experiments  were  conducted  as  follows :  Two  cylinders 
of  sheet  iron  were  made,  one  ten  inches  in  diameter  and  the  other 
fourteen.  They  were  sixteen  inches  high.  The  ten-inch  cylinder, 
after  being  generously  perforated  near  the  bottom,  was  placed 
inside  the  fourteen-inch  cylinder,  the  latter  having  several  deep 
notches  cut  out  at  the  top.  A  cover  of  the  same  material,  and 
fifteen  inches  in  diameter  was  made,  with  a  central  hole  about  two 
and  one-half  inches  in  diameter,  through  which  the  exhaust  pipe 
from  the  engine  could  be  passed.  A  T  was  placed  as  close  to  the 
exhaust  outlet  of  the  engine  as  possible,  and  from  it  one  line  of 
pipe  was  run  directly  to  the  exhaust  muffler,  as  usual,  and  the 
other  line  brought  out  horizontally  and  at  right  angles  to  the  first, 
and  then  directed  downward  to  the  receiver  just  described,  the  end 
of  the  pipe  projecting  about  two  inches  through  the  cover,  into 
the  inside  cylinder.  Fig.  4  gives  a  rough  idea  of  the  arrangement. 

8.  Valves  were  inserted  in  both  pipes,  so  that  the  passage  of 
the  gases  to  the  receiver  or  to  the  muffler  or  to  both  at  once  could 
be  regulated  at  will. 

In  the  receiver  the  gases  were  passed  downward  through  the 
inside  cylinder,  out  through  the  perforations  and  upward  between 
the  two  cylinders,  finally  passing  out  through  the  notches  in  the 
top  of  the  outside  cylinder.  The  object  of  this  arrangement  was 
to  prevent  any  direct  draught  or  chimney  action,  which  would 
cause  an  inrush  of  cold  air  at  the  bottom  as  soon  as  the  inlet  valve 
was  closed.  Two  holes,  large  enough  to  receive  the  thermom- 
eters, were  punched  in  the  cover,  one  midway  between  the 
centre  and  the  inner  wall  and  the  other  about  one-half  inch  from 
the  inner  wall.  There  was  no  expectation  that  temperatures  even 
approaching  correctness  could  be  obtained  by  this  arrangement, 
but  such  a  preliminary  step  was  essential  in  order  to  have  values 
with  which  future  results  could  be  compared. 


DETERMINING   THE   TEMPERATURE   OF   EXHAUST   GASES. 


71 


9.  The  exhaust  was  directed  to  the  receiver,  and  after  being 
allowed  to  flow  until  the  cold  air  in  the  receiver  was  entirely 
expelled,  was  shut  off  and  the  thermometers  quickly  inserted. 
The  gases  were  now  held  in  the  receiver  at  atmospheric  pressure. 
The  pressure  before  closing  the  inlet  was  much  greater,  but 
dropped  almost  instantly  to  that  of  the  atmosphere  when  the 


FIG.  4. 

valve  was  closed.  The  difference  in  the  readings  of  the  two  ther- 
mometers, one  near  the  wall  of  the  cylinder  and  the  other  about 
tAvo  inches  from  the  wall,  was  not  sufficiently  marked  to  be  of 
importance.  The  temperatures  observed  were : 


370  degrees  Fahr. 
395 


394  degrees  Fahr. 

372 

370 


398  degrees  Fahr. 
400 


10.  Various  problems  were  now  to  be  considered.     Radiation 
and  conduction  from  the  cylinders  to  the  outside  air  might  be  so 


72  DETERMINING  THE   TEMPERATURE   OF   EXHAUST   GASES. 

rapid  as  to  vitiate  the  results.  The  thermometers  might  be  af- 
fected by  radiation  from  the  inside  walls.  Radiation  from  the 
iron  exhaust  pipe,  which  projected  into  the  cylinder,  might  make 
the  readings  too  high.  Longer  runs  might  tend  to  cause  the  cylin- 
ders to  store  up  heat. 

Many  such  difficulties  had  to  be  considered,  and,  no  data  being 
found  bearing-  directly  upon  the  subject,  the  experiments  were 
continued. 

An  asbestos  lining  was  now  placed  in  the  outside  cylinder,  and 
the  temperatures  obtained  were : 

474  degrees  Fahr.  511  degrees  Fahr.  52$  degrees  Fahr. 

540        "  552        "  517 

Evidently  the  gases  were  retained  at  a  much  higher  tempera- 
ture than  before,  but  were  these  higher  temperatures  due  to  ex- 
cessive storing  up  of  heat,  or  simply  to  the  prevention  of  excessive 
radiation  ?  A  similar  lining  was  also  placed  in  the  inside  cylinder 
and  the  temperatures  immediately  shot  up  to  over  600  degrees 
Fahr.,  which  were  unquestionably  far  too  high.  In  all  of  the 
above  experiments  radiation  through  the  cover  was  prevented  by 
an  asbestos  lining. 

11.  After  considering  cylinders  of  various  materials,  a  clay 
fire  flue  10  inches  in  diameter  was  secured  and  used  in  place  of 
the  inner  iron  cylinder,  the  outside  iron  cylinder  with  its  asbestos 
lining  being  retained.  The  temperatures  now  recorded  were : 


360  degrees  Fahr.  484  degrees  Fahr.  585  degrees  Fahr. 

498        "          "  560 

512        "          "  564 

541         "  554 

552        "          "  569 

554        "          "  576 


405 
442 
465 
469 


567 


These  figures  seemed  to  indicate  a  gradual  storing  of  heat  from 
the  first  to  about  560  degrees  Fahr.,  when  the  readings  became 
more  constant,  but  not  sufficiently  so  to  warrant  the  conclusion 
that  the  apparatus  was  nearly  correct. 

The  conclusions  at  once  reached  were  that  the  volume  for  the 
gases  was  too  small  and  the  thermometers  too  near  the  walls.  The 
absorbing  of  heat  by  the  receiver  must  also  be  prevented.  In 


DETERMINING   THE   TEMPERATURE   OF   EXHAUST   GASES.  73 

studying  this  problem  it  was  seen  to  be  undesirable  to  allow  the 
gases  to  enter  the  receiver  at  such  high  pressures  and  tempera- 
tures, and  that  it  would  be  of  great  advantage  to  admit  the  gases 
at  a  pressure  and  temperature  little  above  those  desired  at  the  time 
of  reading  the  thermometers.  This  would  do  away  to  a  large 
extent  with  the  tendency  of  the  receiver  walls  to  store  up  heat, 
as  at  no  time  would  they  be  excessively  heated. 

12.  The  proper  throttling  was  secured  by  the  device  shown  in 
Fig.  5. 

It  consists  of  a  2-inch  T  with  a  plug  in  the  top,  through  which 
passes  a  |-inch  bolt,  and  a  nipple  and  cap  in  the  bottom;  the  bolt 


FIG.  5. 

is  supported  by  a  helical  spring,  and  in  turn  supports  at  the  bottom 
a  flat  iron  disk  which  rests  against  the  2-inch  cap — the  bottom  of 
the  cap  being  freely  perforated. 

By  screwing  down  the  nut  at  the  top,  against  the  spring,  any 
desired  resistance  to  the  passage  of  the  gases  can  be  obtained,  and 
at  the  same  time  any  tendency  to  wire-drawing  is  obviated,  as 
would  not  be  the  case  if  the  throttling  were  done  by  means  of  the 
valve  in  the  pipe  alone. 

Before  experimenting  to  any  extent  with  this  device  for  reduc- 
ing the  pressure,  a  new  clay  fire  flue,  18  inches  in  internal  diame- 
ter, with  cover  of  the  same  material,  was  obtained.  In  order  as 
far  as  possible  to  prevent  any  radiation  to  the  thermometer  from 


74  DETERMINING    THE    TEMPERATURE    OF    EXHAUST    GASES. 

the  iron  pipe  delivering  the  gases  to  the  receiver,  the  lower  end 
of  the  device  was  allowed  to  pass  barely  through  the  cover,  ex- 
tending not  over  an  inch  below  the  inner  face. 

13.  The  bottom  of  the  receiver  was  notched  in  several  places 
to  allow  free  passage  of  the  gases  from  within.  The  gases  were 
thus  received  at  the  top,  passing  downward  and  out  at  the  bottom. 


FIG.  6. 


A  rubber  band  3  inches  wide  was  bound  about  the  bottom  of  the 
receiver,  thus  acting  as  a  flap  valve,  the  pressure  of  the  gases 
entering  the  pot  forcing  the  band  outward,  but  the  falling  of  the 
band  preventing  any  inrush  of  cold  air  when  the  admission  of  the 
exhaust  to  the  receiver  was  stopped.  In  Fig.  6  is  shown  the 
completed  receiver  as  attached  to  the  engine. 

Many  series  of  experiments  have  been  carried  on  by  means  of 
this  device,  with  most  satisfactory  results.  With  the  feed  so  ad- 
justed that  the  exhaust  entered  the  receiver  at  a  pressure  but  little 


DETERMINING   THE    TEMPERATURE   OF   EXHAUST    GASES. 


75 


above  that  of  the  atmosphere,  the  storing  of  heat  in  the  walls  was 
practically  prevented. 

14.  In  case  the  exhaust  was  delivered  to  the  receiver  for  an 
hour  or  more  without  ceasing  there  was  a  slight  rise  in  tem- 
perature, but  as  in  practice  the  exhaust  is  cut  off  about  every  10 
minutes  no  difficulty  is  experienced  from  this  cause. 

The  pressure  under  which  the  exhaust  enters  the  receiver  does 
not  have  to  be  closely  regulated,  as  a  slight  difference  does  not 
affect  the  resulting  temperatures,  when  taken  at  atmospheric 
pressure. 

Especially  satisfactory  results  have  been  obtained  when  the 
pressure  was  so  regulated  that  the  temperature  of  the  gases  in 


FIG.  7. 


the  receiver,  while  under  pressure,  was  between  50  degrees  and 
100  degrees  above  the  temperature  at  atmospheric  pressure. 

15.  One  or  two  preliminary  tests  will  quickly  determine  what 
this  temperature  should  be.  The  temperatures  recorded  from  the 
new  receiver  did  not  range  from  400  degrees  Fahr.  to  over  600 
degrees  Fahr.  but  were : 


200  degrees  Fahr. 

195 

195 


202  degrees  Fahr. 

201 

203 


203  degrees  Fahr. 

200 

200 


The  radiation  from  the  receiver  was  not  large.  The  walls  were 
1  inch  thick  and  the  hand  could  at  all  times  be  held  on  the  outside. 

Any  change  in  the  conditions  tending  to  change  the  tempera- 
tures of  the  exhaust  is  quickly  noticed  by  a  corresponding  change 
within  the  receiver.  For  example,  if  the  point  of  ignition  be 
changed,  a  corresponding  change  in  temperatures  is  immediately 


76 


DETERMINING   THE   TEMPERATURE   OF   EXHAUST   GASES. 


observed.     With  the  point  of  ignition  as  shown  by  the  diagram, 
Fig.  7,  the  following  temperatures  were  recorded : 


199  degrees  Fahr. 

198 

198 


197  degrees  Fabr. 

196 

196 


]  97  degrees  Fahr. 

198 

198 


FIG.  8. 


16.  With  the  ignition  retarded  as  shown  by  Fig.  8,  the  tem- 


peratures were : 

210  degrees  Fahr. 

216 

214 


210  degrees  Fahr. 

212 

211 

210 


207  degrees  Fabr. 

212 

209 


While  making  this  particular  series  of  experiments  on  points 
of  ignition,  the  engine  became  stalled  when  set  for  a  certain  point 
of  ignition  and  refused  to  run.  The  igniter  was  removed  and 


FIG.  9. 


found  to  be  badly  burned.     It  was  adjusted  for  sharper  contact 
and  a  new  series  of  readings  taken. 

An  immediate  drop  of  about  50  degrees  in  the  temperature  re- 


DETERMINING   THE   TEMPERATURE   OF   EXHAUST   GASES. 


77 


suited,  showing  at  once  the  quick  response  of  the  receiver  to 
changed  conditions.  The  spark  was  now  sharp  and  short,  while 
previously  the  condition  of  the  sparker  was  such  that  it  was  "  hold- 
ing fire." 

The  new  series  on  the  variation  of  the  point  of  ignition  resulted 


FIG.  10. 


as  follows,  the  temperatures  in  each  column  corresponding  to 
the  point  of  ignition  shown  in  the  diagram  having  the  same  num- 
ber as  the  column  of  temperatures : 


For  Fig.  9. 
151  degrees  Fahr. 
149 
151 
152 
152 


For  Fig.  10. 
166  degrees  Fahr. 
168 
168 
167 
167 


For  Fig.  11. 
172  degrees  Fahr. 
176    " 
178 
175 
178 


17.  Owing  to  the  size  of  the  receiver  and  to  the  necessity  of 
having  other  connections  made  to  the  engine,  the  exhaust  pipe 


FIG.  11. 


leading  to  the  receiver  was  longer  than  desired,  having  a  drop 
of  about  1  foot  and  a  horizontal  length  of  27  inches. 

The  question  of  the  necessity  of  covering  the  pipe,  to  prevent 
excessive  radiation  in  conducting  the  hot  gases  to  the  receiver, 
was  quickly  settled  by  the  following  temperatures  obtained : 


78 


DETERMINING   THE   TEMPERATURE   OF   EXHAUST   GASES. 


Covered. 

155  degrees  Fahr. 
155 

154 
156 

158 
158 
158 
160 


Not  Covered. 
160  degrees  Fahr. 
158 
158 
155 
156 
157 
156 
157 


Having  become  satisfied  that  the  apparatus  as  outlined  was  work- 
ing with  a  reasonable  degree  of  accuracy,  the  next  step  was  to 
devise  a  receiver  which  can  be  erected  quickly  and  cheaply,  as  it 


FIG.  12. 

is  not  always  convenient  to  procure  a  fire  flue  of  the  right  size. 
Accordingly,  a  receiver  was  built  of  ordinary  brick  laid  together 
loosely,  as  shown  in  the  cut,  Fig.  12. 

18.  This  receiver  was  made  of  two  layers  of  brick,  the  inside 
layer  being  laid  on  the  face  and  breaking  joints,  the  outside  layer 
being  laid  on  edge,  thus  breaking  joints  both  vertically  and  horizon- 
tally with  the  inner  layer.  While  the  cracks  furnished  sufficient 
passages  to  prevent  any  overcharging  of  the  receiver,  yet  the  break- 


DETERMINING   THE   TEMPERATURE    OF   EXHAUST   GASES.  79 

ing  of  the  joints  prevented  direct  draughts,  or  inrush  of  cold  air. 
As  first  constructed,  the  volume  of  the  new  receiver  was  made 
equal  to  that  of  the  18-inch  fire  flue  previously  used,  and  the  fire 
flue  cover  was  fitted  to  the  new  receiver.  The  results  were  highly 
satisfactory,  the  temperatures  being  the  same  as  before. 

The-interior  was  then  partially  filled  with  brick  until  the  volume 
was  reduced  from  16  x  16  x  23  to  16  x  16  x  13,  and  again  tested, 
with  the  same  results. 

In  all  of  these  tests  with  the  two  larger  receivers  the  thermom- 
eter bulbs  were  kept  about  4  to  7  inches  away  from  the  walls 
and  from  the  entering  pipe.  In  the  last  receiver,  when  partially 
filled  with  brick,  the  thermometer  bulbs  were  placed  about  the 
same  distance  from  the  cover  and  bottom. 

19.  It  seems  unnecessary,  therefore,  to  have  excessive  volume, 
but  there  must  be  sufficient  space  so  that  the  thermometer  bulbs 
shall  not  be  too  near  the  retaining  walls.     Experiment  indicates 
that  the  figures  suggested  for  these  distances  are  about  right. 

During  the  test  the  valve  leading  to  the  mum er  in  the .  main 
exhaust  is  kept  wide  open,  unless  the  exhaust  pipe  is  larger  than 
is  needed  for  the  quantity  of  exhaust,  and  the  valve  in  the  pipe 
leading  to  the  receiver  is  opened  as  desired.  It  is  necessary  to 
expel  fully  the  cold  air  in  the  receiver  before  any  readings  can 
be  taken. 

With  the  larger  receiver  and  an  8  horse-power  engine  this 
required  about  20  minutes.  The  time  can  be  much  reduced  when 
desired,  by  careful  manipulation  of  the  valves  after  one  becomes 
familiar  with  the  apparatus. 

20.  It  is  of  great  value  to  keep  suspended  within  the  receiver 
at  all  times  a  thermometer  of  sufficient  range  not  to  be  broken 
by  accidental  increase  of  temperature.     In  the  initial  warming 
of  the  receiver  this  thermometer  will  readily  show  when  the  tem- 
perature has  become  constant.     It  also  serves  as  a  very  efficient 
guide  in  adjusting  the  pressure  as  controlled  by  the  inlet.     For 
most  of  the  readings  taken  the  pressure  was  so  regulated  that  this 
permanent  thermometer  recorded,  while  the  gases  were  still  under 
pressure,  temperatures  from  50  degrees  to  70  degrees  Fahr.  higher 
than  the  final  temperatures  at  atmospheric  pressure. 

The  clay  cover  not  being  obtainable  in  all  cases,  gave  way  to 
one  made  of  2-inch  plank,  chinked  with  cotton  waste,  and  this  has 
proved  entirely  satisfactory. 

21.  Previous  methods  of  measuring  the  temperatures  of  the 


80  DETERMINING  THE   TEMPERATURE   OF   EXHAUST   GASES. 

exhaust  have  in  most  cases  furnished  results  which  were  surpris- 
ingly low,  and  not  until  Professor  Robertson's  paper  on  "  An  Effi- 
ciency Test  of  a  One-hundred-and-twenty-five  Horse-power  Gas 
Engine  "  (Vol.  XXI.  Transactions  A.  S.  M.  E.,  p.  396),  has  the 
writer  seen  a  series  of  temperatures  for  the  exhaust,  which  seemed 
reasonably  accurate.  Professor  Robertson  secured  by  means  of  a 
copper-ball  calorimeter  values  above  1,000  degrees  Fahr.,  and  in 
one  instance  records  1,209  degrees  Fahr.,  occasioning  this  remark 
by  Professor  Thurston :  "  The  possibilities  of  still  further  thermo- 
dynamic  gain  are  indicated  by  the  temperature  of  the  exhaust 
gases,  above  1,000  degrees  Fahr.,  and  far  above  that  of  the  prime 
steam  of  our  steam  engines.77 

In  Professor  Robertson's  second  paper  upon  the  same  subject 
(Transactions,  Vol.  XXII.,  p.  612)  he  reports  temperatures  of  the 
exhaust,  as  found  by  a  La  Chatelier  pyrometer,  ranging  from 
1,410  degrees  Fahr.  to  1,805  degrees  Fahr.,  and  states:  "These 
temperatures  appear  to  be  rather  high — so  high  in  fact  that  the 
author  has  examined  other  data  at  hand  to  see  if  any  confirmation 
of  the  above  figures  could  be  found." 

It  is  the  opinion  of  the  writer  that  the  last  figures  quoted  by 
Professor  Robertson  are  not  far  from  correct  for  the  engine 
tested,  but  the  pyrometer  used  is  far  too  expensive  and  requires 
too  much  special  apparatus,  as  well  as  special  calibration,  to  make 
its  use  possible  in  most  tests. 

22.  It  takes  but  a  moment's  consideration  of  the  problem  to 
show  that  very  little  if  any  thermodynamic  gain  is  possible  by 
any  attempted  reduction  of  the  temperatures  of  exhaust,  in  the 
average  gas  engine  of  good  modern  design,  unless  accompanied 
by  a  reduction  of  the  terminal  pressure  as  shown  by  the  expan- 
sion curve. 

23.  With   terminal  pressures   ranging  near    50   pounds   it   is 
quickly  shown  that  the  exhaust  temperatures  must  of  necessity 
be  much  higher  than  generally  recorded.     Suppose,  for  example, 
that  the  expansion  line  of  the  card  shown  in  Fig  9  be  continued 
to  full  cylinder  volume,  as  shown  by  the  point  H. 

The  pressure  at  H  is  found  to  be  50  pounds  absolute.  Suppose 
the  temperature  of  the  mixture  in  the  cylinder,  composed  of  air 
and  gas,  taken  in  during  the  suction  stroke  and  mixed  with  the 
neutral  gases  filling  the  clearance  space,  to  be  only  as  high  as 
that  of  the  room,  say  TO  degrees  Fahr.,  or  529  degrees  absolute 
at  the  point  A,  Fig.  9. 


DETERMINING   THE    TEMPERATURE    OF    EXHAUST    GASES.  81 

Since  the  volume  at  H  is  the  same  as  that  at  A,  the  absolute 
temperatures  will  be  proportioned  to  the  absolute  pressures,  or  if 
Ta  =  absolute  temperature  at  A  =  529  degrees. 
Pa  =  absolute  pressure  at  A  =  14.7  pounds. 
Ph  =  absolute  pressure  at  //  =  50  pounds, 

then  jTA,   the  absolute  temperature  corresponding  to  the  pressure 

2> 
at  H  will  be  derived  from  Th  =  Ta  TT/  Th  =  529fS  =  i;800  de~ 

-*   a 

grees  absolute  or  1,341  degrees  Fahr.  with  the  temperature  of  the 
mixture  taken  at  TO  degrees  Fahr.  only.  Actually  the  tempera- 
ture of  the  mixture  is  much  higher  than  this,  and  by  means  of 
the  new  apparatus  described  in  this  paper  this  temperature  is 
readily  deduced.  The  temperature  secured  at  atmospheric  pres- 
sure by  means  of  the  exhaust  receiver  is  the  temperature  of  the 
neutral  gases  that  fill  the  clearance  space  of  the  cylinder.  The 
method  for  determining  the  temperature  of  the  mixture  after 
having  obtained  the  temperature  of  the  exhaust  gases  is  described 
in  detail  in  paragraph  29  of  paper  No.  0933,  to  be  presented  at 
this  meeting. 
6 


INDEX. 

PAGE 

Introduction iii 

PART  I. 

Air 18 

Cubic  feet  and  cubic  feet  per  hour 20 

Maximum  velocity  of 20 

Specific  heat  of -  21 

Temperature  of 20 

Weight  of 20 

Averages 63 

Brake  work  in  foot  pounds  49 

Brake  work  in  foot  pounds  per  hour 51 

Brake  horse-power 51 

British  thermal  units  equivalent  to 51 

Efficiencies  for : GO,  61 

Brit'sh  thermal  units,  equivalent  to  brake  horse-power 51 

"       equivalent  to  indicated  horse-power 53 

"           "             "       equivalent  to  gas  horse-power 53 

"          "            •'      extracted,  by  observation 57 

"       extracted,  from  indicator  card 57 

"           "             "       supplied,  from  indicator  card. 54 

Cost  per  indicated  horse-power  per  hour 63 

Data  sheet 2 

Efficiencies 60 

Thermal 61 

Thermal  for  brake  horse-power 61 

Thermal  for  indicated  horse-power 61 

Energies 49 

Exhaust 40 

Maximum  velocity  of 43 

Specific  heat  of 43 

Temperature  of 40 

Explosions 12 

Explosions  per  minute 12 

Fuel.... 21 

Cubic  feet,  or  gallons 21 

Maximum  velocity  of 22 

Per  brake  horse-power 62 

Per  indicated  horse-power 62 

Specific  heat  of 22 

Temperature  of  21 

Weight  of S2 


84  INDEX. 

Gas 22,  62 

Standard,  per  hour 22,  62 

Standard,  j  er  brake  horse-power 62 

Standard,  per  indicated  horse-power 62 

Gas  engine  tests , 6,  8,  13 

Data  sheet  of : 2 

Log  of 4 

Report  of 6,  8,  13 

Gas  horse-power 53 

British  thermal  units,  equivalent  to 53 

Heat: 

Absorbed  by  jacket  water 17 

Extracted,  British  thermal  units,  by  observation 57 

"                "             "            "       from  indicator  card 57 

Specific  of  air 21 

Specific  of  exhaust 43 

Specific  of  fuel 22 

Supplied,  British  thermal  units,  from  indicator  card 54 

Heat  balance 63 

Horse-power  : 

brake 51 

British  thermal  units,  equivalent  to  brake 51 

"             "            "       equivalent  to  gas 53 

"             "            "       equivalent  to  indicated 53 

Cost  per  indicated 63 

Fuel  per  brake 62 

Fuel  per  indicated  ...    62 

Gas  53 

Indicated 52 

Indicated  minus  brake  58 

Introductory  remarks    v,  vi 

Indicated  horse-power 52 

British  thermal  units,  equivalent  to 53 

Cost  per  hour  per 63 

Fuel  per  hour  per 62 

Indicated  horse-power — brake  horse-power 58 

Indicator  card 33 

Heat  extracted,  British  thermal  units,  from ...  57 

Heat  supplied,  British  thermal  units,  from   ...    54 

Pressures  from   33 

Ig  Her 2 

Fuel  for 62 

Jacket  water 16 

Heat  absorbed  by 17 

Maximum  velocity  of 17 

Temperature  range  of 16 

Weight  of 16 

Log  of  gas  engine  test 4 

Mechanical  efficiency 60 

Mixture 28 

Maximum  velocity  of 33 


INDEX.  85 

Mixture  : 

Per  cent,  of  throttling  of  entering 59 

Temperature  of 28 

Throttling  of  entering 58 

Weight  of 32 

"n" 23 

Value  of,  in  P  Vn  =  P,  F,» 23 

Object  of  test 6 

Preliminaries  of  test 5 

Pressures  from  indicator  cards 33 

At  end  of  compression 38 

At  end  of  expansion 39 

If  expansion  carried  to  end  of  stroke 39 

Maximum 38 

Mean  effective , 40 

"  R,"  value  of 46 

Revolutions 11 

Revolutions  per  minute 11 

Ratios 43 

Air  to  gas  to  neutrals 43 

Maximum  pressure  to  mean  effective  pressure 45 

Maximum  pressure  to  compression  pressure. 45 

Revolutions  to  explosions 12 

Stroke  to  expansion 44 

Volumes  02  to  Vi 44 

Remarks iii 

Introductory iii 

Report  of  test 6,  8,  13 

Specific  heat 21 

Air 21 

Exhaust 43 

Fuel 22 

Standard  gas 22,  62 

Per  brake  horse-power 62 

Per  indicated  horse-power ...  62 

Per  hour 22,  62 

Time  intervals 11 

Test  : 

Log  of 4 

Object  of 6 

Preliminaries  of 5 

Report  of 6,  8,  13 

Temperature  : 

Air 20 

At  compression 47 

Exhaust 40 

Fuel 21 

Jacket  water 16 

Maximum 47 

Mixture 28 

Thermal  efficiencies. . .  61 


86  INDEX. 

Throttling  of  entering  mixture 58 

Per  cent,  of 59 

Totals , 63 

Velocity 20 

Maximum  for  air 20 

' '        for  exhaust , 43 

"        for  fuel 22 

"        for  mixture 33 

Valve  index  reading 23 

Air 23 

Gas  28 

Water,  jacket 16 

Heat  absorbed  by 17 

Maximum  velocity  of    17 

Temperature  range  of 16 

Weight  of 16 

Weight  : 

Of  air 20 

"exhaust 23 

1 '  fuel 22 

"  mixture 32 

Work: 

Brake  in  foot  pounds 49 

Brake  in  foot  pounds  per  hour 51 

That  would  be  added  if  expansion  were  complete 59 

PAKT  II. 

Covering  pipes 77 

Effect  on  exhaust  temperatures 78 

General  Remarks  and  Method  of  Procedure 67 

Receiver 70,  72 

Forms  of 72,  78 

Size  of ' 73,  79 

Temperatures,  recorded 75,  76,  77,  78 

With  varied  points  of  ignition 76 

Discussion  of  high  exhaust 80 

Thermometers 70,  79 

Positions  of 70,  79 

Throttling  device .    73 


INSTITUTIONS   WITH    WHICH   THE  WRITER    HAS 
BEEN  CONNECTED 

MAINE  STATE  COLLEGE 

UNDERGRADUATE  STUDENT       -  -       1888-1892 

MASSACHUSETTS  INSTITUTE  OF  TECHNOLOGY 

GRADUATE  STUDENT      -  1892-1893 

CASE  SCHOOL  or  APPLIED  SCIENCE 

INSTRUCTOR 1893-1896 

CASE  SCHOOL  OF  APPLIED  SCIENCE 

ASSISTANT  PROFESSOR  -  -  1896-1900 

COLUMBIA  UNIVERSITY 

GRADUATE  STUDENT 19CO-1902 

DEGREES  AND  HONORS  CONFERRED 

B.M.E.  MAINE  STATE  COLLEGE    -       -  1892 

M.E.  CASE  SCHOOL  OF  APPLIED  SCIENCE     -  1898 

FELLOW  COLUMBIA  UNIVERSITY    -       ...  1900 

M.A.  COLUMBIA  UNIVERSITY    -       -       -       -  1901 


SOCIETY  MEMBERSHIP 

AMERICAN  SOCIETY  OF  MECHANICAL  ENGINEERS 
SOCIETY  FOR  THE  PROMOTION  or  ENGINEERING  EDUCATION 


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